METHOD FOR PROCESSING PYROLYSIS OILS FROM PLASTICS AND/OR SOLID RECOVERED FUELS LOADED WITH IMPURITIES

Abstract

The present invention relates to a process for treating an SRF and/or plastics pyrolysis oil, comprising: a) optionally, selective hydrogenation of the feedstock; b) hydroconversion in an ebullated bed, in an entrained bed and/or in a moving bed, to obtain a hydroconverted effluent; c) separation of the hydroconverted effluent in the presence of an aqueous stream, to obtain a gaseous effluent, an aqueous liquid effluent and a liquid hydrocarbon effluent; d) fractionation of the liquid hydrocarbon effluent to obtain at least one gas stream and a cut with a boiling point of less than or equal to 385° C. and a cut with a boiling point above 385° C.; e) hydrotreatment of said cut comprising compounds with a boiling point of less than or equal to 385° C. to obtain a hydrotreated effluent; f) separation to obtain at least a gaseous effluent and a hydrotreated liquid hydrocarbon effluent.

Claims

1. Process for treating a feedstock comprising a solid recovery fuel and/or plastics pyrolysis oil, comprising: a) optionally, a selective hydrogenation step performed in a reaction section fed at least with said feedstock and a gas stream comprising hydrogen, in the presence of at least one selective hydrogenation catalyst, at a temperature of between 100 and 280° C., a partial pressure of hydrogen of between 1.0 and 20.0 MPa abs. and an hourly space velocity of between 0.3 and 10.0 h.sup.−1, to obtain a hydrogenated effluent; b) a hydroconversion step performed in a hydroconversion reaction section, using at least one ebullated-bed reactor, entrained-bed reactor or moving-bed reactor, comprising at least one hydroconversion catalyst, said hydroconversion reaction section being fed at least with said feedstock or with said hydrogenated effluent obtained on conclusion of step a) and a gas stream comprising hydrogen, said hydroconversion reaction section being operated at a temperature of between 250 and 450° C., a partial pressure of hydrogen of between 1.0 and 20.0 MPa abs. and an hourly space velocity of between 0.05 and 10.0 h.sup.−1, to obtain a hydroconverted effluent; c) a separation step, fed with the hydroconverted effluent obtained from step b) and an aqueous solution, said step being performed at a temperature of between 50 and 450° C., to obtain at least one gaseous effluent, an aqueous effluent and a hydrocarbon effluent; d) a step of fractionating all or some of the hydrocarbon effluent obtained from step c), to obtain at least one gas stream, a hydrocarbon cut comprising compounds with a boiling point of less than or equal to 385° C. and a hydrocarbon cut comprising compounds with a boiling point above 385° C., e) a hydrotreatment step performed in a hydrotreatment reaction section, using at least one fixed-bed reactor containing n catalytic beds, n being an integer greater than or equal to 1, each comprising at least one hydrotreatment catalyst, said hydrotreatment reaction section being fed with at least some of said hydrocarbon cut comprising compounds with a boiling point of less than or equal to 385° C. obtained from step d) and a gas stream comprising hydrogen, said hydrotreatment reaction section being operated at a temperature of between 250 and 430° C., a partial pressure of hydrogen of between 1.0 and 20.0 MPa abs. and an hourly space velocity of between 0.1 and 10.0 h.sup.−1, to obtain a hydrotreated effluent; f) a separation step, fed with the hydrotreated effluent obtained from step e) to obtain at least a gaseous effluent and a hydrotreated liquid hydrocarbon effluent.

2. Process according to claim 1, comprising said selective hydrogenation step a).

3. Process according to claim 1, in which the hydrocarbon cut comprising compounds with a boiling point above 385° C. obtained from step d) is at least partly recycled into step b).

4. Process according to claim 1, comprising a step a0) of pretreating the feedstock, said pretreatment step being performed upstream of the optional selective hydrogenation step a) or upstream of the hydroconversion step b) and comprises a filtration step and/or a step of washing with water and/or an adsorption step.

5. Process according to claim 1, in which the hydrotreated liquid hydrocarbon effluent obtained from step f) is sent into a steam cracking step h) performed in at least one pyrolysis furnace at a temperature of between 700 and 900° C. and at a pressure of between 0.05 and 0.3 MPa relative.

6. Process according to claim 1, which also comprises a recycling step g) in which a fraction of the hydrotreated liquid hydrocarbon effluent obtained from the separation step f) is sent into the optional selective hydrogenation step a) and/or the hydroconversion step b) and/or the hydrotreatment step e).

7. Process according to claim 1, in which the separation step f) comprises a fractionation making it possible to obtain, in addition to a gas stream, a naphtha cut comprising compounds with a boiling point of less than or equal to 175° C., and a diesel cut comprising compounds with a boiling point above 175° C. and below 385° C.

8. Process according to claim 1, which also comprises a hydrocracking step e′) performed in a hydrocracking reaction section, using at least one fixed bed containing n catalytic beds, n being an integer greater than or equal to 1, each comprising at least one hydrocracking catalyst, said hydrocracking reaction section being fed at least with said hydrotreated effluent obtained from step e) and/or with the diesel cut comprising compounds with a boiling point above 175° C. and below 385° C. obtained from step f) and a gas stream comprising hydrogen, said hydrocracking reaction section being operated at a temperature of between 250 and 450° C., a partial pressure of hydrogen of between 1.5 and 20.0 MPa abs. and an hourly space velocity of between 0.1 and 10.0 h.sup.−1, to obtain a hydrocracked effluent which is sent into the separation step f).

9. Process according to claim 1, in which the separation step f) also comprises fractionation of the naphtha cut comprising compounds with a boiling point of less than or equal to 175° C. into a light naphtha cut comprising compounds with a boiling point below 80° C. and a heavy naphtha cut comprising compounds with a boiling point of between 80 and 175° C.

10. Process according to claim 9, in which at least part of said heavy naphtha cut is sent to an aromatic complex including at least one naphtha reforming step and/or in which at least part of the light naphtha cut is sent into the steam cracking step h).

11. Process according to claim 1, in which said selective hydrogenation catalyst of step a) comprises a support chosen from alumina, silica, silica-aluminas, magnesia, clays and mixtures thereof and a hydro-dehydrogenating function comprising either at least one group VIII element and at least one group VIB element, or at least one group VIII element.

12. Process according to claim 1, in which, when step b) is performed in an ebullated bed or in a moving bed, said hydroconversion catalyst of step b) comprises a supported catalyst comprising a group VIII metal chosen from the group formed by Ni, Pd, Pt, Co, Rh and/or Ru, optionally a group VIB metal chosen from the group Mo and/or W, on an amorphous mineral support chosen from the group formed by alumina, silica, silica-aluminas, magnesia, clays and mixtures of at least two of these minerals, and when step b) is performed in an entrained bed, said hydroconversion catalyst of step b) comprises a dispersed catalyst containing at least one element chosen from the group formed by Mo, Fe, Ni, W, Co, V and Ru.

13. Process according to claim 1, in which said hydrotreatment catalyst of step e) comprises a support chosen from the group consisting of alumina, silica, silica-aluminas, magnesia, clays and mixtures thereof and a hydro-dehydrogenating function comprising at least one group VIII element and/or at least one group VIB element.

14. Process according to claim 8, in which said hydrocracking catalyst of step e′) comprises a support chosen from halogenated aluminas, combinations of boron and aluminium oxides, amorphous silica-aluminas and zeolites and a hydro-dehydrogenating function comprising at least one group VIB metal chosen from chromium, molybdenum and tungsten, alone or as a mixture, and/or at least one group VIII metal chosen from iron, cobalt, nickel, ruthenium, rhodium, palladium and platinum.

15. Process according to claim 1, in which the feedstock has the following properties: a content of aromatic compounds of between 0 and 90% by weight, a content of halogenated compounds of between 2 and 5000 ppm by weight, a content of metallic elements of between 10 and 10 000 ppm by weight, including a content of iron element of between 0 and 100 ppm by weight, a content of silicon element of between 0 and 1000 ppm by weight.

16. Product which may be obtained via the process according to claim 1.

17. Product according to claim 16, which includes, relative to the total weight of the product: a total content of metal elements of less than or equal to 5.0 ppm by weight, including a content of iron element of less than or equal to 100 ppb by weight, a content of silicon element of less than or equal to 1.0 ppm by weight, a sulfur content of less than or equal to 500 ppm by weight, a nitrogen content of less than or equal to 100 ppm by weight, a content of chlorine element of less than or equal to 10 ppm by weight.

Description

LIST OF FIGURES

[0313] The information regarding the elements referenced in FIG. 1 enables a better understanding of the invention, without said invention being limited to the particular embodiments illustrated in FIG. 1. The various embodiments presented may be used alone or in combination with each other, without any limit to the combinations.

[0314] FIG. 1 represents the scheme of a particular embodiment of the process of the present invention, comprising:

[0315] an optional step a) of selective hydrogenation of a hydrocarbon feedstock obtained from pyrolysis, in the presence of a hydrogen-rich gas 2 and optionally of an amine supplied by the stream 3, performed in at least one fixed-bed reactor including at least one selective hydrogenation catalyst, to obtain an effluent 4; [0316] a step b) of hydroconversion of the effluent 4 obtained from step a), in the presence of hydrogen 5, performed in at least one ebullated-bed, entrained-bed and/or moving-bed reactor including at least one hydroconversion catalyst, to obtain a hydroconverted effluent 6; [0317] a step c) of separation of the effluent 6 performed in the presence of an aqueous washing solution 7, making it possible to obtain at least one fraction 8 comprising hydrogen, an aqueous fraction 9 containing dissolved salts, and a hydrocarbon liquid fraction 10; [0318] a step d) of fractionation of the liquid hydrocarbon fraction 10 making it possible to obtain at least one gaseous fraction 11, a hydrocarbon cut 12 comprising compounds with a boiling point of less than or equal to 385° C. and a hydrocarbon cut 13 comprising compounds with a boiling point above 385° C. which is preferably at least partly recycled into step b); [0319] a step e) of hydrotreatment of at least part of the hydrocarbon cut 12 comprising compounds with a boiling point of less than or equal to 385° C. obtained from step d), in the presence of hydrogen 14, performed in at least one fixed-bed reactor including at least one hydrotreatment catalyst, to obtain a hydrotreated effluent 15; [0320] a step f) of separation of the effluent 15 making it possible to obtain at least one fraction 16 comprising hydrogen and a hydrotreated liquid hydrocarbon effluent 17.

[0321] At the end of step f), at least a part of the hydrotreated liquid hydrocarbon 17 is sent to a steam cracking process (not represented).

[0322] Optionally, part of said hydrotreated liquid hydrocarbon effluent 17 constitutes a recycle stream 17a, 17b and 17c which feeds steps a) and/or b) and/or e), respectively.

[0323] Only the main steps, with the main streams, are shown in FIG. 1, so as to allow a better understanding of the invention. It is clearly understood that all the items of equipment required for the functioning are present (vessels, pumps, exchangers, furnaces, columns, etc.), even if they are not shown. It is also understood that hydrogen-rich gas streams (supply or recycle), as described above, may be injected into the inlet of each reactor or catalytic bed or between two reactors or two catalytic beds. Means well known to those skilled in the art for purifying and recycling hydrogen may also be used.

EXAMPLES

Example 1 (in Accordance with the Invention)

[0324] Feedstock 1 treated in the process is an SRF pyrolysis oil having the characteristics indicated in Table 2.

TABLE-US-00002 TABLE 2 Characteristics of the feedstock Pyrolysis Description Methods Unit oil Density at 15° C. ASTM D4052 g/cm.sup.3 0.91 Sulfur content ISO 20846 ppm by 3500 weight Nitrogen content ASTM D4629 ppm by 2900 weight Acid number ASTM D664 mg KOH/g 15 Bromine number ASTM D1159 g/100 g 60 Diolefin content based on the MAV method weight % 7.0 maleic anhydride value Content of oxygen-based Combustion + weight % 1.0 compounds Infrared Content of paraffins UOP990-11 weight % 15 Content of naphthenes and UOP990-11 weight % 25 olefins Content of aromatics UOP990-11 weight % 60 Content of halogens ASTM D7359 ppm by 400 weight Chloride content ASTM D7536 ppm by 300 weight Content of metals: ASTM D5185 P ppm by 20 weight Fe ppm by 30 weight Si ppm by 500 weight Na ppm by 2 weight B ppm by 2 weight Simulated distillation ASTM D2887  0% ° C. 50 10% ° C. 120 30% ° C. 145 50% ° C. 170 70% ° C. 230 90% ° C. 320 100%  ° C. 405

[0325] The feedstock 1 is subjected directly (without a selective hydrogenation step a)) to a hydroconversion step b) performed in an ebullated bed and in the presence of hydrogen 5 and of a hydrotreatment catalyst of NiMo type on alumina, under the conditions indicated in Table 3.

TABLE-US-00003 TABLE 3 conditions of the hydroconversion step b) Hydroconversion temperature ° C. 400 Partial pressure of hydrogen MPa abs 9.0 H.sub.2/HC (volume coverage of hydrogen Nm.sup.3/m.sup.3 300 relative to the feedstock volume) HSV (flow rate by volume of h.sup.−1 1.0 feedstock/volume of catalysts)

[0326] The effluent 6 obtained from the hydroconversion step b) is sent to step the separation c) and then to the fractionation step d). Table 4 gives the yields of the various fractions obtained at the end of the fractionation step d) relative to the feedstock 1 entering the process chain.

TABLE-US-00004 TABLE 4 yields for the various products and fractions obtained at the end of step b) H.sub.2S + NH.sub.3 weight % 0.35 C1-C4 weight % 3.70 PI-175° C. Fraction weight % 59.0 175° C.-385° C. Fraction weight % 35.0 385° C.+ Fraction weight % 3.0 Total weight % 101.05

[0327] The liquid cut comprising compounds with a boiling point of less than or equal to 385° C. (naphtha cut and diesel cut) is then sent to step e) of hydrotreatmnent and in the presence of hydrogen and of a hydrotreatmnent catalyst of the NiMo type on alumina under the conditions shown in Table 5.

TABLE-US-00005 TABLE 5 conditions of the hydrotreatment step b) Hydrotreatment temperature ° C. 350 Partial pressure of hydrogen MPa abs 9.0 H.sub.2/HC (volume coverage of hydrogen Nm.sup.3/m.sup.3 300 relative to the feedstock volume) HSV (flow rate by volume of h.sup.−1 0.5 feedstock/volume of catalysts)

[0328] The effluent 17 obtained from the hydrotreatment step e) is subjected to a step f) of separation and fractionation.

[0329] Table 6 gives the overall yields relative to the feedstock 1 entering the process chain for the various fractions obtained at the end of the separation and fractionation step f) (which comprises a stripping column and a distillation column).

TABLE-US-00006 TABLE 6 yields for the various products and fractions obtained at the end of step f) H.sub.2S + NH.sub.3 weight % 0.50 C1-C4 weight % 4.50 PI-175° C. Fraction weight % 60.5 175° C.-385° C. Fraction weight % 32.5 385° C.+ Fraction weight % 2.5 Total weight % 100.50

[0330] The compounds H.sub.2S and NH.sub.3 are mainly eliminated in the form of salts in the aqueous phase removed in the separation step d).

[0331] The characteristics of the PI-175° C. and 175° C.-385° C. liquid fractions obtained after the separation and fractionation step f) are shown in Table 7:

TABLE-US-00007 TABLE 7 characteristics of the PI-175° C. and 175° C.-385° C. fractions PI-175° C. 175° C.-385° C. Unit Fraction Fraction Density at 15° C. g/cm.sup.3 0.762 0.813 (ASTM D4052) Content of: Sulfur (ASTM D5453) ppm by <2 <2 weight Nitrogen (ASTM D4629) ppm by <5 <10 weight Fe (ASTM D5185) ppb by Not 25 weight detected Total metals ppm by Not 1 (ASTM D5185) weight detected Chlorine (ASTM D7536) ppb by Not <25 weight detected Paraffins (UOP990-11) weight % 45 30 Naphthenes (UOP990-11) weight % 50 60 Olefins (UOP990-11) weight % 5 10 Aromatics (UOP990-11) weight % 1 2 Simulated distillation (ASTM D2887) in % 0 ° C. 25 175 5 ° C. 38 185 10 ° C. 59 210 30 ° C. 90 240 50 ° C. 118 275 70 ° C. 140 310 90 ° C. 163 360 95 ° C. 175 385 100 ° C. 180 395

[0332] The PH-175° C. and 175° C.-385° C. liquid fractions both have compositions that are compatible with a steam cracking unit, since: [0333] they have very low contents of chlorine element (respectively, an undetected content and a content of 25 ppb by weight), which are below the limit required for a steam cracking feedstock; [0334] the contents of metals, in particular of iron (Fe), are also very low (contents of metals not detected for the PI-175° C. fraction and <1 ppm by weight for the 175° C.-385° C. fraction; [0335] contents of Fe not detected for the PH-175° C. fraction and of 25 ppb by weight for the 175° C.-385° C. fraction), which are below the limits required for a steam cracking feedstock (s 5.0 ppm by weight, very preferably s 1 ppm by weight for metals; s 100 ppb by weight for Fe); [0336] finally, they contain sulfur (<2 ppm by weight for the PI-175° C. fraction and <2 ppm by weight for the 175° C.-385° C. fraction) and nitrogen (<5 ppm by weight for the PI-175° C. fraction and <10 ppm by weight for the 175° C.-385° C. fraction) with contents that are very much lower than the limits required for a steam cracking feedstock (≤500 ppm by weight, preferably 200 ppm by weight for S and N).

[0337] The PI-175° C. and 175° C.-385° C. liquid fractions obtained are thus subsequently sent into a steam cracking step h) (cf. Table 8).

TABLE-US-00008 TABLE 8 conditions of the steam cracking step PI-175° C. 175° C.-385° C. + Unit Fraction Fraction Furnace outlet pressure MPa abs 0.2 0.2 Furnace outlet temperature ° C. 835 820 Steam/feedstock ratio kg/kg 0.6 0.8 Furnace residence time s 0.25 0.2

[0338] The effluents from the various steam cracking furnaces are subjected to a separation step which enables recycling of the saturated compounds into the steam cracking furnaces and the production of the yields presented in Table 9 (yield=mass % of product relative to the mass of the PI-175° C. and 175° C.-385° C. fraction upstream of the steam cracking step, noted as weight %).

TABLE-US-00009 TABLE 9 yields for the steam cracking step PI-175° C. 175° C.-385° C. Fraction Fraction Fraction H.sub.2, CO, C1 weight % 19.0 12.0 Ethylene weight % 33.0 26.0 Propylene weight % 16.0 16.0 C4 cut weight % 9.0 9.0 Pyrolysis gasoline weight % 17.0 19.0 Pyrolysis oil weight % 6.0 18.0

[0339] Considering the yields obtained for the PI-175° C. and 175° C.-385° C. liquid fractions during the pyrolysis oil treatment process at the outlet of the hydroconversion and hydrotreatment steps (cf. Table 6), it is possible to determine the overall yields relative to the feedstock 1 entering the process chain for the products obtained from the steam cracking step h) relative to the initial feedstock of SRF pyrolysis oil type introduced into step a):

TABLE-US-00010 TABLE 10 yields of products obtained from the step of steam cracking of the PI-175° C. fraction and of the 175° C.-385° C. fraction H.sub.2S + NH.sub.3 weight % 0.50 H2, CO, C1 weight % 16.0 C2 weight % 0.6 C3 weight % 1.7 C4 weight % 1.8 Ethylene weight % 28.7 Propylene weight % 15.1 C4 cut weight % 8.4 Pyrolysis gasoline weight % 16.7 Pyrolysis oil weight % 9.5 385° C.+ Fraction weight % 2.5 Total weight % 101.50

[0340] When the PI-175° C. and 175-385° C. fractions are sent to the steam cracking unit, the process according to the invention makes it possible to achieve overall mass yields of ethylene and propylene, respectively, of 28.7% and 15.1% relative to the mass amount of initial feedstock of pyrolysis oil type.

[0341] Furthermore, the specific sequence of steps upstream of the steam cracking step makes it possible to limit the formation of coke and to avoid the corrosion problems which would have appeared had the chlorine not been removed.

Example 2 (in Accordance with the Invention)

[0342] The feedstock 1 treated in the process is a plastics pyrolysis oil having the characteristics indicated in Table 11.

TABLE-US-00011 TABLE 11 feedstock characteristics Pyrolysis Description Methods Unit oil Density at 15° C. ASTM D4052 g/cm.sup.3 0.82 Sulfur content ISO 20846 ppm by 2500 weight Nitrogen content ASTM D4629 ppm by 730 weight Acid number ASTM D664 mg KOH/g 1.5 Bromine number ASTM D1159 g/100 g 80 Diolefin content based on MAV method weight % 10.0 the maleic anhydride value Content of oxygen-based Combustion + weight % 1.0 compounds Infrared Content of paraffins UOP990-11 weight % 45 Content of naphthenes and UOP990-11 weight % 45 olefins Content of aromatics UOP990-11 weight % 10 Content of halogens ASTM D7359 ppm by 350 weight Chloride content ASTM D7536 ppm by 320 weight Content of metals: ASTM D5185 P ppm by 10 weight Fe ppm by 25 weight Si ppm by 45 weight Na ppm by 2 weight B ppm by 2 weight Simulated distillation ASTM D2887  0% ° C. 40 10% ° C. 98 30% ° C. 161 50% ° C. 232 70% ° C. 309 90% ° C. 394 100%  ° C. 432

[0343] The feedstock 1 is subjected to a selective hydrogenation step a) performed in a fixed-bed reactor and in the presence of hydrogen 2 and of a selective hydrogenation catalyst of NiMo type on alumina, under the conditions indicated in Table 12.

TABLE-US-00012 TABLE 12 conditions of the selective hydrogenation step a) Temperature ° C. 180 Partial pressure of hydrogen MPa abs 9.0 H.sub.2/HC (volume coverage of hydrogen Nm.sup.3/m.sup.3 50 relative to the feedstock volume) HSV (flow rate by volume of h.sup.−1 0.5 feedstock/volume of catalysts)

[0344] On conclusion of the selective hydrogenation step a), the diolefin content in the feedstock has been significantly reduced.

[0345] The effluent 4 obtained from the selective hydrogenation step a) is subjected directly, without separation, to a hydroconversion step b) performed in an ebullated bed and in the presence of hydrogen 5 and of a hydrotreatment catalyst of NiMo type on alumina under the conditions presented in Table 13.

TABLE-US-00013 TABLE 13 conditions of the hydroconversion step b) Hydroconversion temperature ° C. 380 Partial pressure of hydrogen MPa abs 9.0 H.sub.2/HC (volume coverage of hydrogen Nm.sup.3/m.sup.3 300 relative to the feedstock volume) HSV (volume flow rate of feedstock h.sup.−1 1.5 in step b)/volume of catalysts)

[0346] The effluent 6 obtained from the hydroconversion step b) is sent to the separation step c) and then to the fractionation step d). Table 14 gives the yields of the various fractions obtained at the end of the fractionation step d) relative to the feedstock 1 entering the process chain.

TABLE-US-00014 TABLE 14 yields for the various products and fractions obtained at the outlet of the fractionation step d) H.sub.2S + NH.sub.3 weight % 0.4 C1-C4 weight % 1.0 PI-150° C. Fraction weight % 28.4 150° C.+ Fraction weight % 70.9 Total weight % 100.7

[0347] The liquid cut comprising compounds with a boiling point of less than or equal to 385° C. (naphtha cut PI-150° C. and diesel cut 150° C.+) is then sent into the hydrotreatment step e) and in the presence of hydrogen and a hydrotreatmnent catalyst of the NiMo on alumina type under the conditions shown in Table 15.

TABLE-US-00015 TABLE 15 conditions of the hydrotreatment step e) Hydrotreatment temperature ° C. 350 Partial pressure of hydrogen MPa abs 9.0 H.sub.2/HC (volume coverage of hydrogen Nm.sup.3/m.sup.3 300 relative to the feedstock volume) HSV (flow rate by volume of h.sup.−1 1 feedstock/volume of catalysts)

[0348] The effluent 17 obtained on conclusion of the hydrotreatmnent step e) is subjected to a step f) of separation and fractionation.

[0349] Table 16 gives the overall yields, relative to the feedstock 1 entering the process chain, for the various fractions obtained at the end of the separation and fractionation step f) (which comprises a stripping column and a distillation column).

TABLE-US-00016 TABLE 16 yields for the various products and fractions obtained at the outlet of the separation and fractionation step f) H.sub.2S + NH.sub.3 weight % 0.5 C1-C4 weight % 1.1 PI-150° C. Fraction weight % 28.6 150° C.+ Fraction weight % 70.7 Total weight % 100.9

[0350] The compounds 1H.sub.2S and NH.sub.3 are mainly eliminated in the form of salts in the aqueous phase removed in the separation step d).

[0351] The characteristics of the PI-150° C. and 150° C.+ liquid fractions obtained after the separation and fractionation step f) are shown in Table 17:

TABLE-US-00017 TABLE 17 characteristics of the PI-150° C and 150° C.+ fractions after step f) of separation and fractionation PI-150° C. 150° C.+ Fraction Fraction Density at 15° C. (ASTM D4052) g/cm.sup.3 0.750 0.820 Content of: Sulfur (ASTM D5453) ppm by <2 <2 weight Nitrogen (ASTM D4629) ppm by <5 <10 weight Fe (ASTM D5185) ppb by Not <50 weight detected Total metals (ASTM D5185) ppm by Not <1 weight detected Chlorine (ASTM D7536) ppb by Not <25 weight detected Paraffins (UOP990-11) weight % 75 70 Naphthenes (UOP990-11) weight % 25 28 Olefins (UOP990-11) weight % Not Not detected detected Aromatics (UOP990-11) weight % <1 2 Simulated distillation (ASTM D2887) in % 0 ° C. 25 140 5 ° C. 32 162 10 ° C. 40 174 30 ° C. 82 226 50 ° C. 108 281 70 ° C. 126 346 90 ° C. 142 395 95 ° C. 146 404 100 ° C. 160 425

[0352] The PI-150° C. and 150° C.+ liquid fractions both have compositions that are compatible with a steam cracking unit, since: [0353] they do not contain any olefins (monoolefins and diolefins); [0354] they have very low contents of chlorine element (respectively, an undetected content and a content of 25 ppb by weight), which are below the limit required for a steam cracking feedstock; [0355] the contents of metals, in particular of iron (Fe), are also very low (contents of metals not detected for the PI-150° C. fraction and <1 ppm by weight for the 150° C.+ fraction; contents of Fe not detected for the PI-150° C. fraction and <50 ppb by weight for the 150° C.+ fraction), which are below the limits required for a steam cracking feedstock (s 5.0 ppm by weight, very preferably ≤1 ppm by weight for metals; s 100 ppb by weight for Fe); [0356] finally, they contain sulfur (<2 ppm by weight for the PI-150° C. fraction and <2 ppm by weight for the 150° C.+ fraction) and nitrogen (<5 ppm by weight for the PI-150° C. fraction and <10 ppm by weight for the 150° C.+ fraction) with contents that are very much lower than the limits required for a steam cracking feedstock (s 500 ppm by weight, preferably s 200 ppm by weight for S and N).

[0357] The PI-150° C. and 150° C.+ liquid fractions obtained are then advantageously sent into a steam cracking step h).