GB1560590A - Process for demetallizing hydrocarbon oils - Google Patents

Description

(54) PROCESS FOR DEMETALLIZING HYDROCARBON OILS (71) We, SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V., a company organised under the laws of The Netherlands, of 30 Carel van Bylandtlaan, The Hague, The Netherlands, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a process for demetallizing hydrocarbon oils by contacting the oils with a catalyst at elevated temperature and pressure and in the presence of hydrogen.

High-boiling-point hydrocarbon oils, such as residual oils obtained in the distillation of crude oils at atmospheric or reduced pressure, as well as certain heavy crude oils, in particular those originating from South America, contain considerable amounts of high-molecular-weight, non-distillable compounds such as asphaltenes and metal compounds, in particular vanadium and nickel compounds. When these high-boiling-point hydrocarbon oils are used as the feed for catalytic processes such as cracking, hydrocracking and hydrodesulphurization, metals such as vanadium and nickel are deposited on the catalyst particles. As a result of the increasing vanadium and nickel concentration on the active sites of the catalyst, a rapid deactivation of the catalyst occurs.

To increase catalyst life it has already been proposed to remove the metals from the feed before the latter is contacted with the metal-sensitive catalyst. This may be effected by contacting the feed with a suitable demetallization catalyst at elevated temperature and pressure and in the presence of hydrogen. For this purpose various catalysts have already been proposed consisting of a porous material which may comprise one or more metals having hydrogenation activity.

An investigation by the Applicant into the hydrodemetallization of hydrocarbon oils having a total vanadium and nickel content of more than 250 ppmw with the aid of catalysts having a surface area of at most 100 m2/g has shown that good catalysts for this purpose have to meet a number of requirements with regard to porosity and particle size. These requirements are partly dependent on the hydrogen partial pressure at which the hydrodemetallization is carried out. A good catalyst for the hydrodemetallization of hydrocarbon oils having a total vanadium and nickel content of more than 250 ppmw within the scope of this patent application is a catalyst whose demetallization activity is of a sufficiently high level when half the catalyst life has elapsed and which, moreover, has a sufficiently high metal uptake capacity.

It has been found that for the catalytic hydrodemetallization of hydrocarbon oils having a total vanadium and nickel content of more than 250 ppmw with the aid of a catalyst having a surface area of at most 100 m2/g, the requirements with respect to porosity and particle size which a good catalyst should meet are as follows. The catalysts should have a total pore volume (VT) above 0.2 ml/g and they should have a specific average particle diameter (d) of at least 0.4 and at most 5 mm. Further, the catalysts should have such an average pore diameter (p*), VT and d that the following requirement is met:

where PH represents the hydrogen partial pressure applied (p* in nm, d in mm, VT in ml/g, PH. in bar). The above-mentioned values of d and p* have been defined as follows on the basis of their method of determination.

The way in which d is determined depends on the shape of the catalyst particles. If the shape is such that the particle diameter distribution of the catalyst can be determined with the aid of a sieve analysis, d is determined as follows. After a complete sieve analysis of a representative catalyst sample has been carried out, d is read from a graph in which for each successive sieve fraction the percentage by weight, based on the total weight of the catalyst sample, has been cumulatively plotted as a function of the linear average particle diameter of the relevant sieve fraction; d is the particle diameter corresponding to 50% of the total weight. This method can be used to determine d of spherical and granular materials and materials with a similar shape, such as extrudates and pellets having a length/diameter ratio between 0.9 and 1.1. The determination of d of extrudates and pellets having a length/diameter ratio smaller than 0.9 or larger than 1.1 and of similar cylindrically shaped materials, whose particle diameter distribution cannot be determined with the aid of a sieve analysis, is carried out as follows. After a complete length distribution analysis (if the length/diameter ratio is smaller than 0.9) or after a complete diameter distribution analysis (if the length/diameter ratio is larger than 1.1) of a representative catalyst sample has been carried out, d is read from a graph in which for each successive length and diameter fraction, respectively, the percentage by weight, based on the total weight of the catalyst sample, has been cumulatively plotted as a function of the linear average size of the relevant fraction; d is the value corresponding to 50% of the total weight.

After a complete pore diameter distribution of a catalyst sample has been determined, p* is read from a graph in which for each successive pore volume increment smaller than or equal to 10% of the pore volume, the quotient of the pore volume increment and the corresponding pore diameter interval has been cumulatively plotted as a function of the linear average pore diameter over the relevant pore diameter interval; p is the pore diameter corresponding to 50% of the total quotient.

A determination of the complete pore diameter distribution of the catalyst may very suitably be carried out with the aid of the nitrogen adsorption/desorption method (as described by E.V. Ballou and O.K. Doolen in Analytical Chemistry 32, 532 (1960)) combined with the mercury penetration method (as described by H.L. Ritter and L.C.

Drake in Industrial and Engineering Chemistry, Analytical Edition 17, 787 (1945)), applying mercury pressures of 1-2000 bar. In this case, the pore diameter distribution of the catalyst in the pore diameter range below and including 7.5 nm is calculated from the nitrogen desorption isotherm (assuming cylindrical pores) according to the method described by J.C.P. Broekhoff and J.H. de Boer in Journal of Catalysis 10, 377 (1968) and the pore diameter distribution of the catalyst in the pore diameter range above 7.5 nm is calculated with the aid of the formula: pore diameter (in nm) = 15000 absolute mercury pressure (in bar) The nitrogen pore volume and the total pore volume mentioned in this patent application are determined as follows. The nitrogen pore volume of a catalyst is the pore volume determined with the aid of the above-mentioned nitrogen adsorption/desorption method.

The total pore volume of a catalyst is the sum of the nitrogen pore volume present in pores with a diameter below and including 7.5 nm (determined with the aid of the above-mentioned nitrogen adsorption/desorption method) and the mercury pore volume present in pores with a diameter above 7.5 nm (determined with the aid of the above-mentioned mercury penetration method). The surface areas mentioned in this patent application have been determined according to the B.E.T. method.

The present invention therefore relates to a process for demetallizing hydrocarbon oils by contacting the oils with a catalyst at elevated temperature and pressure and in the presence of hydrogen, the hydrocarbon oil to be treated having a total vanadium and nickel content of more than 250 ppmw, while a catalyst is used which meets the above-mentioned requirements.

Very suitable materials to be used as catalysts or catalyst carriers in the process according to the invention are oxides of the elements of Groups II, III and IV of the Periodic Table of Elements or mixtures of the said oxides, such as silica, alumina, magnesia, zirconia, boria, silica-alumina, silica-magnesia and alumina-magnesia.

Another type of material that is very suitable to serve as the catalyst or catalyst carrier in the process according to the invention is soot, in particular a soot obtained as a by-product in the partial oxidation of hydrocarbons with air, oxygen or mixtures of air and oxygen, either in the presence or in the absence of steam.

As catalysts or catalyst carriers for the process according to the invention aluminas, silicas and silica-aluminas are preferred. Very suitable catalysts or catalyst carriers are alumina or silica particles prepared by spray-drying of an alumina or silica gel, followed by shaping of the spray-dried micro particles into larger particles, e.g. by extrusion, and spherical alumina or silica particles obtained by the well-known oil drop method. The latter method comprises formation of an alumina or silica hydrosol, combining the hydrosol with a gelating agent and dispersing the mixture as droplets in an oil which may be kept at an elevated temperature; the droplets remain in the oil until they have solidified to form spherical hydrogel particles, which are subsequently separated, washed, dried and calcined. Very suitable silica-alumina catalysts or catalyst carriers are cogels of aluminium hydroxide gel on silica hydrogel.

The present catalysts or catalyst carriers may, inter alia, be shaped by extrusion or pelletizing. In addition to these shaping techniques especially the well-known nodulizing method is a very attractive shaping technique for the present catalysts or catalyst carriers.

According to this method catalyst particles having a diameter of at most 0.1 mm are agglomerated with the aid of a granulation liquid to form particles having a diameter of at least 1.0 mm.

The catalysts that are used in the process according to the invention may be promoted with one or more metals having hydrogenation activity. When using promoted catalysts preference is given to catalysts comprising 0.1-15 pbw of the said metals per 100 pbw carrier. The metals having hydrogenation activity are preferably selected from nickel, cobalt, molybdenum, vanadium and tungsten. It is further preferred that the catalyst should comprise at least one metal selected from nickel and cobalt and at least one metal selected from molybdenum, vanadium and tungsten and further that the atomic ratio between nickel and/or cobalt on the one hand and molybdenum, vanadium and/or tungsten on the other hand is between 0.05 and 3.0. Suitable metal combinations are nickel-vanadium, cobalt-molybdenum, nickel-molybdenum and nickel-tungsten.

The metal load of the catalysts applied according to the invention preferably amounts to 0.5-10 pbw and in particular 2.0-7.5 pbw per 100 pbw carrier. Especially preferred catalysts according to the invention are catalysts comprising about 1/2 pbw nickel and about 2 pbw vanadium per 100 pbw carrier, as well as catalysts comprising about 1 pbw nickel or cobalt and about 4 pbw molybdenum per 100 pbw carrier. The metals may be present on the carrier in the metallic form or in the form of their oxides or sulphides. Preference is given to catalysts in which the metals are present on the carriers in the form of their sulphides.

When the process according to the invention is used for hydrodemetallizing hydrocarbon oils having a total vanadium and nickel content of more than 1000 ppmw, which hydrocarbon oils are selected from crude oils and topped crude oils, preference is given to a catalyst which meets the following requirements (1) VT is larger than 0.6 ml/g, (2) d is at least 1.5 and at most 3 mm, and (3) after substitution of d, VT and PH2 in the formula ln * 1.4 x PH2)2 d VT (7 it is found that p* must be larger than a certain value Q expressed in nm; in the present case p* should have a value which is larger than Q + 10 nm.

The above-mentioned preference for catalysts for hydrodemetallizing hydrocarbon oils having a total vanadium and nickel content of more than 1000 ppmw applies to promoted catalysts as well as to non-promoted catalysts.

The demetallization activity of the present catalysts may be increased by the addition of hydrogen sulphide. Therefore, the process according to the invention is preferably carried out with addition of hydrogen sulphide. A further investigation concerning the influence of the addition of hydrogen sulphide when using the present catalysts for demetallizing heavy hydrocarbon oils has shown that the effect of hydrogen sulphide greatly depends on the hydrogen partial pressure and the total pressure applied. When the point of view is taken that the use of hydrogen sulphide in the demetallization is economically attractive in particular when, at a given total pressure, it results in a gain in demetallization activity of more than 50%, then it is found that this requirement can be met if the quantity of hydrogen sulphide is chosen such that the quotient PH2S/PH2 iS equal to at least 4 200 and at moss 2PT-60 PT + (PT)2 and at most Put+60 Within the limits set by the formula the demetallization activity of the catalysts reaches an optimum value at a certain PH3S (P*H1/4S). The value of P* s is different for the different catalysts and can be determined from some tentative experiments. Application of a PH > S above or below P*H2S but within the limits given, still results in an increase of the demetallization activity by more than 50%, but this increase is smaller than the attainable maximum.

Obviously, during the demetallization process P*H.S or any other PH.S may be controlled by continuously supplying a sufficient quantity of hydrogen sulphide from an external source to the oil to be demetallized. However, from an economic point of view it is more attractive to utilize to the largest possible extent the hydrogen sulphide which is released in the demetallization process and/or in a desulphurization process carried out on oil which has been treated by the demetallization process. This consideration led to the following three attractive embodiments of the demetallization process according to the invention in the presence of additional hydrogen sulphide.

1) Application of gas recirculation in the demetallization process, the largest possible portion of hydrogen sulphide being left in the recirculating gas until the desired PH2S is reached. A certain quantity of hydrogen sulphide is thereupon continuously removed from the recirculating gas to maintain the desired hydrogen sulphide concentration.

2) In particular when a high PH3S is desired, it may take a considerable time before the hydrogen sulphide concentration in the recirculating gas has reached the desired value. This difficulty can be met by supplying hydrogen sulphide from an external source during the initial stage of the process and gradually reducing the supply of hydrogen sulphide as the process advances. This additional quantity of hydrogen sulphide may, for instance, come from a hydrodesulphurization process.

3) Instead of gas recirculation to the demetallization reactor or in combination with it, offgas from a desulphurization reactor installed after the demetallization reactor is used as the feed gas for the demetallization reactor. A process scheme for a combined demetallization/desulphurization process in the presence of hydrogen, which scheme is based on the aforementioned principle, is shown in the attached figure and is further elucidated hereinafter.

The plant comprises successively a hydrodemetallization unit (1), a first gas-liquid separation unit (2), a hydrodesulphurization unit (3), a second gas-liquid separation unit (4) and a unit for the removal of hydrogen sulphide (5). A metal- and a sulphur-containing residual hydrocarbon oil (6) is subjected to hydrodemetallization together with two hydrogen- and hydrogen- sulphide-containing gas streams (7) and (8) and, if desired, with a hydrogen sulphide stream (9) from an external source. The product so obtained (10) is separated into a low-metal liquid stream (11) and a hydrogen- and hydrogen-sulphidecontaining gas stream (7), the latter being recycled to the demetallization unit. Liquid stream (11) is subjected to hydrodesulphurization together with a hydrogen-containing gas stream (12) and a hydrogen stream (13) from an external source. The product so obtained (14) is separated into a low-metal and low-sulphur liquid stream (15) and a hydrogen- and hydrogen-sulphide-containing gas stream (16), the latter being split into two portions (8) and (17) of the same composition. Portion (8) is recycled to the demetallization unit and portion (17), after removal of hydrogen sulphide, is recycled to the desulphurization unit as a gas stream (12).

The process according to the invention is preferably carried out by passing the hydrocarbon oils at elevated temperature and pressure and in the presence of hydrogen in an upward, a downward or a radial direction through one or more vertically disposed reactors containing a fixed or moving bed of the catalyst particles concerned. The process may, for instance, be carried out by passing the hydrocarbon oils together with hydrogen through a vertically disposed catalyst bed in an upward direction, the liquid and gas velocities applied being such as to cause the catalyst bed to expand (processing in ebullated bed operation). A very attractive embodiment of the process is one in which the hydrocarbon oil is passed through a vertically disposed catalyst bed, in which during operation fresh catalyst is periodically introduced at the top of the catalyst bed and spent catalyst is withdrawn at the bottom thereof (processing in bunker flow operation). Another very attractive embodiment of the process is one in which several reactors each containing a fixed catalyst bed are used, which reactors are alternately used for the process concerned; while the process is carried out in one or more of these reactors, the catalyst in the other beds is replenished (processing in fixed-bed swing operation). If desired, the process may also be carried out by suspending the catalyst in the hydrocarbon oil to be treated (processing in slurry phase operation).

The process according to the invention is preferably carried out at a temperature of 350-450"C, a hydrogen partial pressure of 25-200 bar and a space velocity of 0.1-10 kg.kg-l.h-l. Special preference should be given to the following conditions: a temperature of 375-425"C, a hydrogen partial pressure of 50-150 bar and a space velocity of 0.5-5 kg.kg-l.h-l. Hydrodemetallizing of metal-containing hydrocarbon oils is particularly important if the oil is subsequently subjected to catalytic cracking, hydrocracking or hydrodesulphurization. As a result of the hydrometallization deactivation of the catalysts used in these processes is suppressed to a considerable extent. Hydrocracking and hydrodesulphurization of hydrocarbon oils may be carried out by contacting the oils at elevated temperature and pressure and in the presence of hydrogen with a suitable catalyst which may be present in the form of a fixed bed, a moving bed or a suspension of catalyst particles. An attractive combination of demetallization according to the invention and hydrocracking or hydrodesulphurization is one in which the demetallization is carried out in fixed-bed swing operation or in bunker flow operation, while hydrocracking or hydrodesulphurization is carried out in conventional fixed-bed operation.

Examples of hydrocarbon oils having a total vanadium and nickel content of more than 250 ppmw which are eligible for demetallization according to the invention are crude oils and residues obtained in the distillation of crude oils such as topped crude oils, long residues and short residues.

The invention will now be elucidated with the aid of the following examples.

Example 1 Residual hydrocarbon oil having a total vanadium and nickel content of 1250 ppmw, which oil had been obtained after topping and dewatering of a crude oil from South America, was catalytically hydrodemetallized using nine different non-promoted catalysts.

To this end the oil, together with hydrogen, was passed downwards through a cylindrical vertically disposed fixed catalyst bed at a temperature of 410"C, a hydrogen partial pressure (measured at the reactor inlet) of 150 bar, a space velocity of 2.1 kg of fresh feed per kg of catalyst per hour and a gas rate of 1000 N1 H2/kg of fresh feed. The liquid reaction product was split into two portions of the same composition in a volume ratio of 22:1. The smaller portion was removed from the system and the larger portion was recycled to the reactor inlet.

The results of the demetallization experiments together with the properties of the catalysts applied have been collected in Table A. For determining p 3 and the total pore volume use was made of the nitrogen adsorption/desorption method and of the mercury penetration method, as stated hereinbefore.

Table A Exp. Catalyst p*, nm d, mm Total Surface Vmax, k1.5 pore area, volume, kg.kg-1.h-1 No. ml/g m/g %w (ppmw V)- 1 SiO2-Al2O3 40 2.4 0.60 50 35 0.14 2 SiO2 33 3.5 0.80 70 32 0.15 3 SiO2 57 2.4 0.75 63 45 0.15 4 SiO2 40 2.4 0.90 66 42 0.14 5 Al2O3 320 2.4 0.90 32 55 0.10 6 SiO2 1650 2.4 0.90 2 56 0.10 7 Al2O3 48 5.5 0.25 95 16 0.10 8 SiO2 20 2.4 0.45 90 20 0.15 9 Al2O3 53 1.5 0.15 15 10 0.06 The performance of the catalyst is assessed on the basis ov Vmax and k1.5. Vmax is the maximum quantity of vanadium, expressed in %w on fresh catalyst, which the catalyst particles can absorb in their pores and k1.5 is the activity of the catalyst, expressed in kg.kg-1.h043. (ppmw V)-, after half the catalyst life (in terms of quantity of vanadium absorbed) has elapsed. k1.5 is calculated with the formula k1.5 = (space velocity in kg.kg-1.h-1) X ppmw V in feed - ppmw V in product (ppmw V in product) 1 The performance of a catalyst is rated good under the conditions applied in this demetallization is the criteria are met that Vmax is larger than 30 %w and that k1.5 is larger than 0.08 kg.kg-1.h-1. (ppmw V)-.

The performance of a catalyst is rated excellent under the conditions applied in thiy demetallization, if the criteria are met that Vmax is larger than 40 %w and that k1.5 is larger than 0.08 kg.kg-1.h-1. (ppmw V)-.

Experiments 1-6 in which the above conditions with respect to Vmax and k1.5 were satisfied, are demetallization experiments according to the invention. In these experiments where catalysts were used with PH2 1n p* 1.4 )2, > X ( # d VT 150 these catalyst also met the additional requirements of the invention with respect to surface area (# 100 m/g), VT ( > 0.2 ml/g) and (0.4-5 mm.). In Experiments 3-6, catalysts were used which, in addition, also met the additional requirements with respect to p* ( > Q + 10 nm), VT ( > 0.6 ml/g) and d (1.5-3 mm), which, according to the invention, rank as excellent catalysts.

Experiments 7-9, in which the above conditions with respect to Vmax and kl.5 were not satisfied, are demetallization experiments outside the scope of the present invention. In Experiments 7-9 catalysts were used which did not satisfy the condition 1n p* 1.4 (PH2)2.

#d > VT x 150 Moreover, in Experiment 7 the catalyst used had a d > 5 mm and in Experiment 9 a catalyst was used with a VT < 0.2 ml/g.

Example II Experiment 4 of Example I was repeated several times, each time with application of a different hydrogen sulphide partial pressure. In these experiments hydrogen sulphide was added from an external source. In all experiments a constant total pressure (measured at the reactor inlet) of 150 bar was applied. The results of these experiments have been collected in Table B.

Table B Exp. PH2, PH2s, k15, Gain kg.kh-1.h-1 in k1.5 No. bar bar (ppmw V)- % 4 150 0 0.14 10 147 3 0.17 21 11 140 10 0.24 71 12 125 25 0.32 129 13 95 55 0.22 57 In Experiments 11-13 a PH2S/PH2 was applied satisfying the relation 4 200 2PT-60 PT + (PT) # PH2S/PH2 # PT+60 , and a gain in demetallization activity of more than 50% was reached. In Experiment 10 a PH,s/PH was applied which did not satisfy the above-mentioned relation and a gain in demetallization activity of less than 50% was obtained.

Claims (18)

WHAT WE CLAIM IS:

1. A process for demetallizing hydrocarbon oils, characterized in that hydrocarbon oils with a total vanadium and nickel content of more than 250 ppmw are contacted, at elevated temperature and pressure and in the presence of hydrogen, with a catalyst meeting the following requirements: 1n p* 1.4 PH2 (1) #d > VT x (150 ) where p* represents the average pore diameter in nm, d the specific average particle diameter in mm, VT the total pore volume in ml/g and PH2 the hydrogen partial pressure applied in bar, (2) the surface is at most 100 m2/g, (3) VT is larger than 0.2 ml/g, and (4) d is at least 0.4 and at most 5 mm.

2. A process according to claim 1, characterized in that as the catalyst or as catalyst carrier is used an oxide of an element of Group II, III or IV or a mixture of the said oxides.

3. A process according to claim 2, characterized in that as the catalyst or catalyst carrier silica, alumina or silica-alumina is used.

4. A process according to any one of claims 1-3, characterized in that a catalyst is used which is promoted with 0.5-10 pbw and preferably with 2.0-7.5 pbw metals having hydrogenating activity per 100 pbw carrier.

5. A process according to any one of claims 1-4, characterized in that a catalyst is used which is promoted with at least one metal selected from nickel and cobalt and at least one metal selected from molybdenum, vanadium and tungsten.

6. A process according to any one of claims 1-5, characterized in that it is carried out in bunker flow operation or in fixed-bed swing operation.

7. A process according to any one of claims 1-6, characterized in that for hydrodemetallizing hydrocarbon oils having a total vanadium and nickel content of more than 1000 ppmw, which hydrocarbon oils have been selected from crude oils and topped crude oils, a catalyst is used which meets the following requirements: (1) VT is larger than 0.6 ml/g (2) d is at least 1.5 and at most 3 mm, and (3) after substitution of d, VT and PH in the formula Th* 1.4 > c PH d z VT ^ also it is found that p* must be larger than a certain value Q expressed in nm; in the present case * should have a value which is larger than Q + 10 nm.

8. A process according to any one of claims 1-7, characterized in that it is carried out with addition of hydrogen sulphide.

9. A process according to claim 8, characterized in that it is carried out in the presence of such a quantity of hydrogen sulphide that the quotient PH2S/PH2 satisfies the relation: 4 200 2PT-60 PT + (PT) #PH2S/PH2 # PT+60 , where PH. PH.S and PT represent the hydrogen partial pressure, the hydrogen sulphide partial pressure and the total pressure in bar. respectively.

10. A process according to claim 8 or 9, characterized in that in the process use is made of hydrogen sulphide which is released in the demetallization process and/or in a desulphurization process carried out on oil which has been treated by, the demetallization process.

11. A process according to claim 10, characterized in that gas recirculation is applied in the demetallization process, the largest possible portion of hydrogen sulphide being left in the recirculating gas until the desired PH,S is reached, after which a certain quantity of hydrogen sulphide is continuously removed from the recirculating gas to maintain the desired hydrogen sulphide concentration.

12. A process according to claim 11, characterized in that during the initial stage of the process hydrogen sulphide from an external source is supplied to the process and that the quantity of the hydrogen sulphide supplied is gradually reduced as the process advances.

13. A process according to claim 10, characterized in that a metal- and a sulphurcontaining residual hydrocarbon oil is subjected to hydrodemetallization together with two hydrogen- and hydrogen-sulphide-containing gas streams (A and B) and, if desired, with a hydrogen sulphide stream from an external source, that the product obtained is separated into a low-metal liquid stream and a hydrogen- and hydrogen-sulphide-containing gas stream, the latter being recycled as gas stream A to the demetallization reactor, that the low-metal liquid stream together with a hydrogen-containing gas stream (C) and a hydrogen stream from an external source are subjected to hydrodesulphurization, that the product obtained is separated into a low-metal and a low-sulphur liquid stream and a hydrogen- and hydrogen-sulphide-containing gas stream, the latter being split into two portions of the same composition, that one of these portions is recycled to the demetallization reactor as gas stream B and that the other portion after removal of hydrogen sulphide is recycled to the desulphurization reactor as gas stream C.

14. A process for the catalytic conversion of metal-containing hydrocarbon oils by cracking, hydrocracking or hydrodesulphurization, the oil first being demetallized and then being catalytically converted, characterized in that the demetallization is carried out according to any one of claims 1-13.

15. A process according to any one of claims 1-14, characterized in that it is carried out at a temperature of 350-450"C, a hydrogen partial pressure of 25-200 bar and a space velocity of 0.1-10 kg.kg-1.h-l.

16. A process according to claim 15, characterized in that it is carried out at a temperature of 375-425"C, a hydrogen partial pressure of 50-150 bar and a space velocity of 0.5-5 kg.kg-l.h-l.

17. A process for demetallizing hydrocarbon oils, substantially as described hereinbefore and in particular with reference to the examples as far as they refer to Experiments 1 to 6 and 10-13.

18. Demetallized hydrocarbon oils obtained according to claim 17.