Method for converting a high-boiling hydrocarbon feedstock into lighter boiling hydrocarbon products

Abstract

The present invention relates to a process for converting a high-boiling hydrocarbon feedstock into lighter boiling hydrocarbon products, said lighter boiling hydrocarbon products being suitable as a feedstock for petrochemicals processes, said converting process comprising the following steps of: feeding a hydrocarbon feedstock having a boiling point of >350 deg Celsius to a cascade of hydrocracking unit(s), feeding the bottom stream of a hydrocracking unit as a feedstock for a subsequent hydrocracking unit, wherein the process conditions in each hydrocracking unit(s) are different from each other, in which the hydrocracking conditions from the first to the subsequent hydrocracking unit(s) increase from least severe to most severe, and processing the lighter boiling hydrocarbon products from each hydrocracking unit(s) as a feedstock for one or more petrochemicals processes.

Claims

1. A process for converting a high-boiling hydrocarbon feedstock into lighter boiling hydrocarbon products, said lighter boiling hydrocarbon products being suitable as a feedstock for petrochemicals processes, said process comprising the steps of: feeding a hydrocarbon feedstock having a boiling point of greater than 350 C. to a hydrotreating unit which yields a bottom stream having a boiling point of greater than 350 C. and consisting essentially of hydrocarbons, wherein the hydrocarbon feedstock consists essentially of hydrocarbons; feeding the bottom stream from of the hydrotreating unit to a first hydrocracking unit of a cascade of hydrocracking units comprising at least two hydrocracking units under conditions to produce a first hydrocracked bottom stream having a boiling point of greater than 350 C. that consists essentially of hydrocarbons, and a first lighter boiling fraction with a boiling point of less than 350 C., wherein the first hydrocracking unit is a fixed bed reactor; wherein the catalyst in the first hydrocracking unit comprises at least one member selected from the group consisting of sulphided NiW, precious metal hydrogenation functions supported on Al.sub.2O.sub.3 or Al.sub.2O.sub.3/Halogen base material, and wherein the first hydrocracking step is operated to achieve from 50 to 70% conversion as calculated by the portion of the bottom stream of the hydrotreating unit converted into products with boiling points below 350 C.; feeding the bottom stream of said first hydrocracking unit to a second hydrocracking unit to produce a second lighter boiling fraction and also a hydrocracked bottom fraction consisting essentially of hydrocarbons and a second lighter boiling fraction, wherein the second hydrocracking unit is an ebullating bed reactor; wherein the operating pressure for the first hydrocracking stage is 150 to 200 Barg operating pressure and the operating pressure for the second hydrocracking stage is 100 to 200 Barg; wherein the feedstock of the second hydrocracking unit is heavier than the feedstock of the first hydrocracking unit; wherein the process conditions in the first hydrocracking unit is less severe than the second hydrocracker; wherein the temperature prevailing in said hydrotreating unit is higher than in said first hydrocracking unit, wherein the temperature in said hydrotreating unit is in the range 300 to 400 C. and the temperature in said first hydrocracking unit is in the range 280 to 300 C.; wherein the second lighter boiling fraction comprises C2 to <350 C. boiling range hydro-cracking products; wherein the temperature in the cascade of hydrocracking units increases from said first hydrocracker unit to said second hydrocracker unit; and processing the fraction with a boiling point of less than 350 C. from the first hydrocracker and the top fraction from the second hydrocracking unit as a feedstock for a petrochemical process; separating the first and second lighter boiling hydrocarbon fractions into (i) a first stream containing the unused hydrogen, possible H.sub.2S, NH.sub.3, H.sub.2O, and methane and (ii) a second stream comprising C2 and C2+ products with boiling points below 350 C.; wherein the particle size of the catalyst present decreases from the first hydrocracking unit to the second hydrocracking unit; and wherein the first stream is returned to a hydrocracking unit, wherein the petrochemical process comprises at least one member selected from the group consisting of alkylation units, isomerization units and reforming units, or combinations thereof; and the process includes a third hydrocracking unit downstream from the second hydrocracking unit and wherein the reactor design of the a third hydrocracking unit is chosen from the group of a the fixed bed reactor, an ebullated bead reactor, a slurry reactor and a slurry phase reactor and wherein hydrocracking in the third hydrocracking unit is conducted at 490 C.

2. The process according to claim 1, wherein the temperature in said hydrotreating unit is 300 C. and the temperature in said first hydrocracking unit is 300 C.

3. The process according to claim 1, wherein the temperature in said hydrotreating unit is 400 C. and the temperature in said first hydrocracking unit is 300 C.

4. The process according to claim 1, wherein the temperature in said hydrotreating unit is 400 C.

5. The process according to claim 1, wherein the third hydrocracking unit is an ebullated bed reactor.

6. The process according to claim 1, wherein the hydrocarbon feedstock to at least one of said first hydrocracking unit or said second hydrocracking unit further comprises a heavy stream originating from a steam cracker unit.

7. A process for converting a high-boiling hydrocarbon feedstock into lighter boiling hydrocarbon products, said lighter boiling hydrocarbon products being suitable as a feedstock for petrochemicals processes, said process consisting of the following steps of: feeding a hydrocarbon feedstock having a boiling point of >350 deg Celsius to a hydrotreater operated at a temperature to produce a hydrotreated bottom stream, wherein the feedstock consists of a bio-based material; feeding the hydrotreated effluent to a cascade of hydrocracking units comprising at least three hydrocracking units, wherein the bottom stream of said first hydrocracking unit is used as a feedstock for said second hydrocracking unit, the bottom stream of said second hydrocracking unit is used as a feedstock for said third hydrocracking unit, wherein the pressure for the first hydrocracking stage is 150 to 200 Barg operating pressure, the pressure for the second hydrocracking stage is 100 to 200 Barg operating pressure and the pressure for the third hydrocracking stage is 100 to 300 Barg operating pressure, wherein the bottom stream of a hydrocracking unit as a feedstock for a subsequent hydrocracking unit is such that said feedstock for a subsequent hydrocracking unit is heavier than the feedstock of a previous hydrocracking unit in the cascade of hydrocracking units, wherein the process conditions in each hydrocracking unit is different from each other, in which the hydrocracking conditions from the first to the subsequent hydrocracking unit increase from least severe to most severe, wherein the temperature prevailing in said hydrotreating unit is higher than in said first hydrocracking unit, wherein the temperature in said hydrotreating unit is in the range 300 to 400 C. and the temperature in said first hydrocracking unit is in the range 280 to 300 C., wherein the temperature in the cascade of hydrocracking units increases, wherein the temperature prevailing in said third hydrocracking unit is higher than in said hydrotreating unit, wherein the temperature in said third hydrocracking unit consists of 490 C., and processing lighter boiling hydrocarbon products from each hydrocracking units as a feedstock for one or more petrochemicals processes.

8. A process consisting of the steps of: separating crude oil in a distillation tower to yield a heavy crude fraction the heavy crude fraction having a boiling point greater than 350 C. and a light crude fraction having boiling point of less than 350 C.; feeding the heavy crude fraction to a hydrotreater which fixed bed reactor containing a hydrotreating catalyst consisting of combination of sulphided Co/Mo/Al.sub.2O.sub.3, Ni/W/Al.sub.2O.sub.3 and Ni/Mo/Al.sub.2O.sub.3 catalysts to hydrotreating the heavy fraction and obtain a first effluent, wherein the catalysts are 1.5 to 3 mm diameter cylindrical tablets or extrudates, and wherein the operating conditions for hydrotreating include a pressure of 150 Barg, a Liquid Hourly Space Velocity (LHSV) of 0.25 hr.sup.1, a Start of Run Inlet Temperature of 350 C. and a Start of Run Exit Temperature 390 C.; directly feeding the first effluent in a separator to obtain a first lights fraction and a first heavy fraction having a boiling point of greater than 350 C.; separating the first lights fraction into a fraction consisting of C2 hydrocarbons, a fraction consisting of C3 hydrocarbons, and a faction consisting of C4 hydrocarbons; feeding the first heavy fraction to a first hydrocracker containing a first catalyst consisting of sulphided NiW, metallic Pd and metallic Pt on an Al.sub.2O.sub.3/halogen support and hydrocracking the heavy fraction to obtain a first hydrocracker products stream and a first hydrocracker residue, wherein operating conditions in the first hydrocracker include a first hydrocracker operating pressure of 150 to 200 Barg; a first hydrocracker Start of Run Inlet Temperature of from 280 C. to 300 C., and a first hydrocracker Start of Run Exit Temperature 330-350 C. and a moderate LHSV of 2-4 hr.sup.1; feeding first products stream to a flash distillation vessel to obtain a gas stream containing unused hydrogen, H.sub.2S, NH.sub.3, H.sub.2O and methane and a stream comprising C2 or larger hydrocarbons; feeding the first hydrocracker residue to a second hydrocracker and hydrocracking the first hydrocracking residue to form a second hydrocracker reaction products stream and a second hydrocracker residue stream comprising material boiling over 350 C., wherein the second hydrocracker contains a second catalyst, wherein the second catalyst has a particle size of about 0.8 mm, and wherein the processing conditions in the second hydrocracker include a second hydrocracker reactor temperature between 420 and 450 C., a second hydrocracker operation pressure between 100 and 200 Barg and a second hydrocracker LHSV between 0.1 and 1.5 Hr.sup.1; separating the second reaction products stream to obtain a second gas stream containing unused hydrogen and methane and a second stream comprising C2 or larger hydrocarbon products with boiling points below 350 C.; feeding the second hydrocracker residue stream to a third hydrocracker comprising a third catalyst, and hydrocracking the second hydrocracker residue stream to obtain a third reaction products stream; feeding the third products reaction stream to a separator to obtain a third gas stream containing unused hydrogen and methane and a third stream comprising C2 or larger hydrocarbon products with boiling points below 350 C.; sending residue from the third hydrocracker to a separator to obtain a purge stream and a third hydrocracker heavy residue, and recycling the third hydrocracker heavy residue to the third hydrocracking unit; wherein the third catalyst consists of nano-sized catalyst particles consisting of MoS.sub.2 wherein operating parameters in the third hydrocracking unit include a third hydrocracking temperature of 490 C. and third hydrocracking operating pressure between 100 and 300 Barg.

Description

(1) FIG. 1 shows an embodiment of the present invention, comprising a cascade of two hydrotreating units.

(2) FIG. 2 shows another embodiment of the present invention, comprising a cascade of three hydrotreating units preceded by a hydrotreating unit.

(3) The reference signs in both FIG. 1 and FIG. 2 do not relate with each other.

EXAMPLE 1

(4) The process scheme according to Example 1 can be found in FIG. 1. It is clear for the person skilled in the art that commonly used process equipment like compressors, heat exchangers, pumps, tubing etc. has been omitted due to maintain the legibility of the scheme itself. The process scheme comprises two different stages, i.e. a first hydrocracking stage 2 and a second hydrocracking stage 3.

(5) Crude oil 14 coming from a tank 11 is separated in a separator 1, for example distillation tower, and its heavy fraction 9 having a boiling point of >350 deg Celsius is sent to a cascade of hydrocracking units 2,3. It should be noted that the presence of separator 1 is not a stipulation in terms of processing hydrocarbon feedstock according to the present method.

(6) In the first hydrocracking unit 2 the feedstock 18 is cracked in the presence of hydrogen in a fraction 17 having a boiling point of >350 deg Celsius and a fraction 15 having a boiling point of <350 deg Celsius. Fraction 17 is the feedstock for second hydrocracking unit 3. Fraction 15 is separated in separator 6 into gas stream 19 containing the unused hydrogen together with and H2S, NH3 and H2O together with any methane produced and a stream 21 comprising any C2 or larger hydrocarbon products with boiling points below 350 C., wherein stream 21 can be further separated in specific components, like C2/C3/C4 etc.

(7) In the hydrocracking unit 2 moderate cracking is preferred together with a high degree of hydrogenation to prepare a feed suitable for cracking to extinction in the second step of the hydrocracking cascade. Consequently catalysts incorporating sulphided NiW or precious metal hydrogenation functions supported on Al2O3 or Al2O3/Halogen base materials are preferred. The first step might be operated to achieve 50 to 70% conversion as calculated by the portion of feed material 18 converted into products with boiling points below 350 C.

(8) Fraction 17 is fed to a second hydrocracker 3 and further cracked in the presence of hydrogen resulting in a fraction 23 having a boiling point of >350 deg Celsius and a fraction 16 having a boiling point of <350 deg Celsius. Fraction 16 is separated in separator 7 in a gas stream 20 containing the unused hydrogen together with and H2S, NH3 and H2O together with any methane produced and a stream 22 comprising any C2 or larger hydrocarbon products with boiling points below 350 C., wherein stream 22 can be further separated in specific components, like C2/C3/C4 etc.

(9) The majority of the metal containing hetero-atomic species present in the feed 17 to the cascade hydrocracker units 2, 3 would be decomposed to hydrocarbon species and the resultant metals would be deposited on the catalyst causing some deactivation. As the sum of the Ni and V metal content in this stream is reasonably low the rate of catalyst deactivation would be low enough to allow practical operating cycles. The operating cycle for this step on the cascade hydrocracker could, however, be extended by allowing for on-stream catalyst replacement e.g. by having two or more parallel reactors operated in a swing mode with periodic catalyst replacement in the off-stream.

(10) The >350 C. boiling point product stream 17 from the first unit 2 in the cascade would be fed, together with hydrogen (not shown), to the second hydrocracking unit 3. This latter processing step could be carried out in either an ebullated bed or a slurry phase hydrocracker. These types of hydrocracking technologies are preferred as the species present in the feed stream are large molecules which diffuse poorly within the pore structure of catalyst particles and as such catalysts with a high ratio of external to internal area (such as the catalysts suitable for use in ebullated bed and slurry phase hydrocracking reactors) are preferred. In this processing step a high degree of cracking is required to minimize or eliminate the need for a residue recycle or purge stream. For this reason catalysts with relatively high cracking activity such as those using SiO2/Al2O3 and/or acid forms of zeolites are preferred. A moderate level of hydrogenation activity is sufficient for this catalyst hence catalysts containing sulphided NiMo and or sulphided NiW would be suitable.

(11) In an embodiment (not shown) stream 21 and stream 22 can be collected and further processed. Stream 21 and 22 can be used as a feedstock for one or more petrochemicals processes.

(12) The residue 23 coming from second hydrocracker unit 3 is sent to a separator 10 and separated into unconverted heavy residue 4 and heavy residue 12, wherein heavy residue 12 is recycled to unit 3. Such a recycle can include a complete recycle or a recycle of some parts.

(13) In a specific embodiment (not shown) stream 20 containing the unused hydrogen together with and H2S, NH3 and H2O together with any methane produced can be sent to a previous hydrocracking unit, that is here unit 2, in stead of to the same unit that is here unit 3.

(14) In a specific embodiment (not shown) the hydrocarbon feed to the hydrocracking 2 comprises not only heavy fraction 9 but other type of feedstock 8 as well. Examples of feedstock 8 are tar sand oil, shale oil and bio based materials. It is also possible to feed feedstock 5 directly into hydrocracking unit 3. The type of feedstock 5 can be tar sand oil, shale oil and bio based materials as well. The conditions in hydrocracking unit 2 and 3 are as follows: suitable operating conditions for the 1st hydrocracking unit 2 would be chosen to achieve a high degree of hydrogenation and a moderate degree of cracking activity. Suitable conditions, in combination with previously mentioned catalyst types, would include: 150 to 300 Barg operating pressure; Start of Run Reactor Temperature between 300 C. and 330 C. and a moderate LHSV of 2-4 hr-1. Suitable operating conditions for the 2nd hydrocracking unit 3 would be chosen to achieve a high degree of cracking activity. Suitable conditions, in combination with previously mentioned catalyst types, would include a reactor temperature between 420 and 450 C, operation pressure between 100 and 200 Barg and an LHSV between 0.1 and 1.5 hr-1.

EXAMPLE 2

(15) The process scheme according to Example 2 can be found in FIG. 2. It is clear for the person skilled in the art that commonly used process equipment like compressors, heat exchangers, pumps, tubing etc. has been omitted due to legibility of the scheme itself. The process scheme comprises four different stages, i.e. a hydrotreating stage 2, a first hydrocracking stage 3, a second hydrocracking stage 4 and a third hydrocracking stage 5.

(16) Hydrotreating Stage

(17) As the residue fraction of crude oil typically contains significant quantities of heteroatom (e.g. sulphur, nitrogen and metals such as nickel and vanadium) containing species, the first stage in the proposed cascade-hydrocracking process is designed to carry out much of the hydro-desulphurisation, hydro-denitrogenation etc. as well as a small amount of hydrocracking (i.e. the breaking of carbon-carbon bonds in association with the addition of hydrogen). The present hydrotreating stage utilizes a combination of sulphided Co/Mo/Al2O3, Ni/W/Al2O3 and Ni/Mo/Al2O3 catalysts (typically as 1.5 to 3 mm diameter cylindrical tablets or extrudates), usually, in fixed bed reactors (trickle bed in residue hydrotreating).

(18) Typical operating conditions used for hydrotreating atmospheric residue (i.e. the crude oil cut boiling above 350 C.) are reported (Ref. table 18.18 Page 339 of the Handbook of Commercial Catalysts-Heterogeneous Catalysts, Howard F. Rase, CRC Press) to be: Pressure 150 Barg, Liquid Hourly Space Velocity (LHSV) 0.25 hr{circumflex over ()}1, Start of Run Inlet Temperature 350 C., Start of Run Exit Temperature 390 C.

(19) Whilst the non-metal hetero-atoms (S, N, O etc.) are removed as gaseous compounds (e.g. H2S, NH3, H2O respectively) metallic heteroatoms removed from the feed stream are deposited on the catalyst and cause deactivation. For this reason there might be present a system to allow deactivated catalysts to be replaced whilst the plant remains on line. These systems can involve the use of two or more reactors operated in a swing mode (i.e. one reactor is in operation whilst the other reactor is off-line for a catalyst change and when the catalyst in the first reactor becomes sufficiently deactivated the reactors are swapped over). The Axens HYVAL-S process is an example of this type of process. Another technique used to allow the replacement of deactivated catalyst is to continuously or periodically discharge a portion of the catalyst bed from the base of the reactor(s) and add fresh catalyst to the top of the reactor(s). This is achieved by the use of a series of valves on the top and base of the reactor(s).

(20) Although not limiting, crude oil 14 coming from a tank 11 is first separated in a separator 1, for example distillation tower, and its heavy fraction 27 having a boiling point of >350 deg Celsius is sent to a hydrotreating unit 2 and a cascade of hydrocracking units 3, 4, 5. It should be noted that the presence of separator 1 is not a stipulation in terms of processing hydrocarbon feedstock according to the present method. Heavy fraction 27 can be further treated in unit 13, but unit 13 is optional.

(21) In the hydrotreating unit 2 the feed 25 is converted in a lights fraction 17 and a heavy fraction 21 having a boiling point of >350 deg Celsius. In separator 6 fraction 17 is further separated in a recycle gas stream 30 and a gaseous fraction 34 comprising any C2 or larger hydrocarbon products with boiling points below 350 C., wherein stream 34 can be further separated in specific components, like C2/C3/C4 etc. The heavy fraction 21 is sent to the first hydrocracking unit 3.

(22) First Hydrocracking Stage

(23) The reactor effluent 21 from the hydrotreating step 2 in the cascade is passed directly to the first hydrocracking unit 3. In the first hydrocracking unit 3 the reaction products stream 18 is sent to a separator 7 (e.g. flash distillation vessel) which splits the reaction products stream 18 into (i) a gas stream 31 containing the unused hydrogen together with and H2S, NH3 and H2O together with any methane produced and (ii) a stream 35 comprising any C2 or larger hydrocarbon products with boiling points below 350 C. The heavy fraction stream 22 comprising any material boiling above 350 C. is used as a feedstock for the subsequent hydrocracking unit 4. The purpose of the first step in the hydrocracking cascade is to break down a portion of the >350 C. boiling range the molecules into smaller, lower boiling point materials, that are suitable for feeding to a steam cracker to make olefins, whilst minimizing the production of methane. Useful dual functional catalysts contain components active for carbon-carbon bond scission (cracking) and hydrogenation. It is reported (Ref. Page 347 of the Handbook of Commercial CatalystsHeterogeneous Catalysts, Howard F. Rase, CRC Press) that a range of catalysts compositions are suitable for use in hydro-cracking including: For the hydrogenation function in order of increasing activity under low-sulphur conditions: sulphided NiMo, sulphided NiW, metallic Pd and metallic Pt. For the cracking function Al2O3, Al2O3/halogen, SiO2/Al2O3 and acid forms of zeolites. The selection of the most suitable catalyst type depends on the intended extent of reaction.

(24) In the first hydrocracking reactor of a cascade hydrocracker it would be desirable to select a catalyst with a high degree of hydrogenation activity together with a low to moderate degree of cracking activity (to minimize the extent of methane formation). Such a catalyst might be based on sulphided NiW, metallic Pd or metallic Pt together with an Al2O3 or Al2O3/halogen support.

(25) Suitable process conditions for first hydrocracking step in the cascade hydrocracker might be selected to promote a high degree of hydrogenation and only a moderate level of cracking (to minimize methane formation): Suitable operating conditions, therefore might be: 150 to 200 Barg operating pressure; Start of Run Inlet Temperature 280300 C., Start of Run Exit Temperature 330-350 C. and a moderate LHSV of 2-4 hr-1.

(26) Second Hydrocracking Stage

(27) The reactor effluent 22 from the first hydrocracking unit 3 in the cascade will be sent to a second hydrocracking unit 4. The reaction products stream 19 is passed into a separator 8 which splits the reaction products stream 19 into (i) a gas stream 32 containing the unused hydrogen together with any methane produced in the first hydrocracking step which can largely be recycled to the reactor and (ii) a stream 36 comprising any C2 or larger hydrocarbon products with boiling points below 350 C. The stream 23 comprising any material boiling above 350 C. is used as a feedstock for the third hydrocracking unit 5 the purpose of which would be to break down a portion of the >350 C. boiling range the molecules into smaller, lower boiling point materials, that are suitable for feeding to for example a steam cracker to make olefins, whilst minimizing the production of methane. This feed material contains significant quantities of large molecules and has a high viscosity hence, to ensure good contact between the catalyst and these molecules a small catalyst particle size is desirable together with an ebullated bed reactor design. Processes using small particle sized catalyst (0.8 mm) with compositions similar to those used for fixed bed hydrocracking processes are preferred. In the second step in the hydrocracking cascade process it may be desirable to select a catalyst with a higher cracking activity than was selected for the first step. Consequently a catalyst using a siO2/Al2O3 or zeolite component may be preferred.

(28) Suitable process conditions for such a processing step would be a reactor temperature between 420 and 450 C, operation pressure between 100 and 200 Barg and an LHSV between 0.1 and 1.5 Hr-1.

(29) Third Hydrocracking Stage

(30) The reactor effluent 23 from the second hydrocracking step in the cascade is sent to a third hydrocracking unit 5. The reaction products stream 20 will be passed into a separator 9 which splits the reaction products stream 20 into (i) a gas stream 33 containing the unused hydrogen together with any methane produced in the previous hydrocracking step which can largely be recycled to the reactor and (ii) a stream 37 comprising any C2 or larger hydrocarbon products with boiling points below 350 C. The stream 24 comprising any material boiling above 350 C. can be fed to another hydrocracking step, or can be used for other purposes.

(31) The residue 24 coming from third hydrocracker unit 5 can also be sent to a separator 10 and separated in purge stream 29 and heavy residue 28, wherein heavy residue 28 is recycled to unit 5. Feed material 23 contains significant quantities of large and very difficult to hydrocrack molecules and has a high viscosity hence, to ensure good contact between the catalyst and these molecules a very small catalyst particle size is desirable together with slurry reactor design.

(32) Suitable catalysts use very small, colloidal or even nano-sized catalyst particles comprised of such materials as MoS2 and have operating temperatures between 440 and 490 C. and operating pressures between 100 and 300 Barg.

(33) The reactor effluent 20 from the third hydrocracking step in the cascade would be passed into a separator 9 which splits the effluent into (i) a gas stream 33 containing the unused hydrogen together with any methane produced which can largely be recycled to the reactor and (ii) and a separate stream 37 comprising any C2 or larger hydrocarbon products with boiling points below 350 C. The stream 24 comprising any material boiling above 350 C. can be further separated in a separator 10, wherein stream 28 can be recycled to the slurry reactor where it can be mixed with the stream passing forward from the second hydrocracking step.

(34) A small purge stream may be utilized to remove the spent catalyst and some small fraction of the heavy (i.e. BP>350 C.) reactor effluent.

(35) In a specific embodiment (not shown) stream 32, 33 containing the unused hydrogen together with and H2S, NH3 and H2O together with any methane produced can be sent to a previous hydrocracking unit, that is here unit 3 for stream 32 and unit 4 for stream 33, respectively.

(36) In a specific embodiment (not shown) the hydrocarbon feed to the hydrocracking unit 3 comprises not only heavy fraction 21 but feedstock 15 as well. Such a construction also holds for unit 4 and 5 with feed 12 and 16, respectively. Examples of feedstock 12, 15, 16 are tar sand oil, shale oil and bio based materials. It is also possible to feed a feedstock 26 directly in hydrotreating unit 2.

(37) The conditions in hydrocracking unit 3, 4 and 5 are comparable to those earlier mentioned.

(38) The particle size of the catalysts present in units 3, 4, 5 decreases in size, that is the particle size of catalyst in unit 5, is smaller than that in unit 3.

(39) For legibility purposes both in FIG. 1 and FIG. 2 the separators 6,7,8,9 have been shown as units separate from the reactor units 2,3,4,5, respectively. However, one can understand that a stream coming from the respective hydrocracking unit is sent to one or more separators for obtaining a stream containing the unused hydrogen together with any methane produced, another stream comprising any C2 or larger hydrocarbon products with boiling points below 350 C. and a stream comprising any material boiling above 350 C. The present method is however not restricted to the specific construction shown in FIG. 1 and FIG. 2.