METHOD FOR THE TREATMENT OF PLASTIC PYROLYSIS OILS INCLUDING TWO-STAGE HYDROCRACKING

Abstract

The present invention relates to a process for treating a plastics pyrolysis oil, comprising: a) the selective hydrogenation of said feedstock to obtain a hydrogenated effluent; b) hydrotreatment of said hydrogenated effluent to obtain a hydrotreatment effluent; c) a first step of hydrocracking of said hydrotreated effluent to obtain a first hydrocracked effluent; d) separation of the hydrocracked effluent in the presence of an aqueous stream, to obtain a gaseous effluent, an aqueous liquid effluent and a hydrocarbon-based liquid effluent; e) fractionation of the hydrocarbon-based liquid effluent to obtain at least one gas stream and at least one naphtha cut and a heavier cut; f) a second step of hydrocracking of the heavier cut to obtain a second hydrocracked effluent; g) recycling of at least a portion of said second hydrocracked effluent into the separation step d).

Claims

1. Process for treating a feedstock comprising a plastics pyrolysis oil, comprising: a) 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 10.0 MPa abs. and an hourly space velocity of between 0.3 and 10.0 h.sup.−1, to obtain a hydrogenated effluent; b) a 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 at least with said hydrogenated effluent obtained from step a) and a gas stream comprising hydrogen, said hydrotreatment reaction section being used at a temperature of between 250 and 430° C., a partial pressure of hydrogen of between 1.0 and 10.0 MPa abs. and an hourly space velocity of between 0.1 and 10.0 h.sup.−1, to obtain a hydrotreatment effluent; c) a first hydrocracking step performed in a hydrocracking 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 hydrocracking catalyst, said hydrocracking reaction section being fed at least with said hydrotreated effluent obtained from step b) and a gas stream comprising hydrogen, said hydrocracking reaction section being used at a temperature of between 250 and 480° C., a partial pressure of hydrogen of between 1.5 and 25.0 MPa abs. and an hourly space velocity of between 0.1 and 10.0 h.sup.−1, to obtain a first hydrocracked effluent; d) a separation step, fed with the hydrocracked effluent obtained from step c) and an aqueous solution, said step being performed at a temperature of between 50 and 370° C., to obtain at least one gaseous effluent, an aqueous effluent and a hydrocarbon-based effluent; e) a step of fractionating all or a portion of the hydrocarbon-based effluent obtained from step d), to obtain at least one gas stream and at least two liquid hydrocarbon-based streams, said two liquid hydrocarbon-based streams being at least one naphtha cut comprising compounds with a boiling point of less than or equal to 175° C. and one hydrocarbon cut comprising compounds with a boiling point of greater than 175° C.; f) a second step of hydrocracking performed in a hydrocracking 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 hydrocracking catalyst, said hydrocracking reaction section being fed with at least a portion of said hydrocarbon cut comprising compounds with a boiling point of greater than 175° C. obtained from step e) and a gas stream comprising hydrogen, said hydrocracking reaction section being operated at a temperature of between 250 and 480° C., a partial pressure of hydrogen of between 1.5 and 25.0 MPa abs. and an hourly space velocity of between 0.1 and 10.0 h.sup.−1, to obtain a second hydrocracked effluent; g) a step of recycling at least a portion of said second hydrocracked effluent obtained from step f) into the separation step d).

2. Process according to claim 1, which also comprises a recycling step h) in which a fraction of the hydrocarbon-based effluent obtained from the separation step d) or a fraction of the naphtha cut with a boiling point of less than or equal to 175° C. obtained from the fractionation step e) is sent into the selective hydrogenation step a) and/or the hydrotreatment step b).

3. Process according to claim 1, in which the amount of the recycle stream from step h) is adjusted so that the weight ratio between the recycle stream and the feedstock comprising a plastics pyrolysis oil is less than or equal to 10.

4. Process according to claim 1, comprising a step a0) of pretreating the feedstock comprising a plastics pyrolysis oil, said pretreatment step being performed upstream of the selective hydrogenation step a) and comprising 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 reaction section of step a) or b) uses at least two reactors functioning in permutable mode.

6. Process according to claim 1, in which a stream containing an amine is injected upstream of step a).

7. Process according to claim 1, in which said selective hydrogenation catalyst 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.

8. Process according to claim 1, in which said hydrotreatment catalyst 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.

9. Process according to claim 1, in which said hydrocracking catalyst of step c) or of step f) comprises a support chosen from halogenated aluminas, combinations of boron and aluminum 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.

10. Process according to claim 1, in which said zeolite is chosen from Y zeolites, alone or in combination, with other zeolites from among beta, ZSM-12, IZM-2, ZSM-22, ZSM-23, SAPO-11, ZSM-48 and ZBM-30 zeolites, alone or as a mixture.

11. Process according to claim 1, in which the naphtha cut comprising compounds with a boiling point of less than or equal to 175° C. obtained from step e), is sent, totally or partly, into a steam cracking step i) 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.

12. Process according to claim 1, in which the naphtha cut comprising compounds with a boiling point of less than or equal to 175° C. obtained from step e) is fractionated into a heavy naphtha cut comprising compounds with a boiling point of between 80 and 175° C. and a light naphtha cut comprising compounds with a boiling point of less than 80° C., at least a portion of said heavy cut being sent into an aromatic complex including at least one naphtha reforming step.

13. Process according to claim 12, in which at least a portion of the light naphtha cut is sent into the steam cracking step i).

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

Description

LIST OF FIGURES

[0207] 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.

[0208] FIG. 1 represents the scheme of a particular embodiment of the process of the present invention, comprising:

[0209] a step a) of selective hydrogenation of a hydrocarbon-based feedstock obtained from the pyrolysis of plastics 1, 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; [0210] a step b) of hydrotreatment of the effluent 4 obtained from step a), in the presence of hydrogen 5, performed in at least one fixed-bed reactor including at least one hydrotreatment catalyst, to obtain a hydrotreated effluent 6; [0211] a first step c) of hydrocracking of the effluent 6 obtained from step c), in the presence of hydrogen 7, performed in at least one fixed-bed reactor including at least one hydrocracking catalyst, to obtain a first hydrocracked effluent 8; [0212] a step d) of separation of the effluent 8 performed in the presence of an aqueous washing solution 9, making it possible to obtain at least one fraction 10 comprising hydrogen, an aqueous fraction 11 containing dissolved salts, and a hydrocarbon-based liquid fraction 12; [0213] a step e) of fractionating the hydrocarbon-based liquid fraction 12 making it possible to obtain at least one gaseous fraction 13, a naphtha cut 14 comprising compounds with a boiling point of less than or equal to 175° C. and a cut 15 comprising compounds with a boiling point of greater than 175° C.; [0214] a second step f) of hydrocracking at least a portion of the cut 15a comprising compounds with a boiling point of greater than 175° C. obtained from step e), in the presence of hydrogen 16, performed in at least one fixed-bed reactor including at least one hydrocracking catalyst, to obtain a second hydrocracked effluent 17; the other portion of the cut 15 constitutes the purge 15b; [0215] a step of recycling the second hydrocracked effluent 17 into the separation step d).

[0216] Instead of injecting the amine stream 3 into the inlet of the selective hydrogenation step a), it is possible to inject it into the inlet of the hydrotreatment step b), into the inlet of the hydrocracking step c), into the inlet of the separation step d) or else not to inject it, depending on the characteristics of the feedstock.

[0217] On conclusion of step e), at least a portion of the naphtha cut 14 comprising compounds with a boiling point of less than or equal to 175° C. is sent into a steam cracking process (not shown).

[0218] Optionally, a portion of the naphtha cut 14 comprising compounds with a boiling point of less than or equal to 175° C. obtained from step e) constitutes a recycle stream which feeds the selective hydrogenation step a) (fraction 14a), and the hydrotreatment step b) (fraction 14b).

[0219] 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 equipment required for the functioning is present (vessels, pumps, exchangers, furnaces, columns, etc.), even if it is 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)

[0220] The feedstock 1 treated in the process is a plastics pyrolysis oil (i.e. comprising 100% by weight of said plastics pyrolysis oil) having the characteristics indicated in Table 2.

TABLE-US-00002 TABLE 2 feedstock characteristics Description/ Methods Unit Pyrolysis oil Density at 15° C. ASTM D4052 g/cm.sup.3 0.820 Sulfur content ISO 20846 ppm by weight 2500 Nitrogen content ASTM D4629 ppm by weight 730 Acid number ASTM D664 mg KOH/g 1.5 Bromine content ASTM D1159 g/100 g 80 Content of diolefins MAV method.sup.(1) Weight % 10 from the maleic anhydride number Content of oxygen Combustion + Weight % 1.0 compounds infrared Content of paraffins U0P990-11 Weight % 45 Content of naphthenes U0P990-11 Weight % 20 Content of olefins U0P990-11 Weight % 25 Content of aromatics U0P990-11 Weight % 10 Content of halogens ASTM-D7359 ppm by weight 350 Content of asphaltenes IFP9313 ppm by weight 380 Chloride content ASTM D7536 ppm by weight 320 Content of metals: ASTM-D5185 P ppm by weight 10 Fe ppm by weight 25 Si ppm by weight 45 Na ppm by weight 2 B ppm by weight 2 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 [0221] (1) MAV method described in the article: C. López-García et al., Near Infrared Monitoring of Low Conjugated Diolefins Content in Hydrotreated FCC Gasoline Streams, Oil & Gas Science and Technology—Rev. IFP, Vol. 62 (2007), No. 1, pages 57-68

[0222] The feedstock 1 is subjected to a selective hydrogenation step performed a) 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 3.

TABLE-US-00003 TABLE 3 conditions of the selective hydrogenation step a) Temperature ° C. 180 Partial pressure of hydrogen MPa abs 6.4 H.sub.2/HC (volume coverage of hydrogen Nm.sup.3/m.sup.3 50 relative to the feedstock volume) HSV (volume flow rate of feedstock/ h.sup.−1 0.5 volume of catalysts)

[0223] On conclusion of the selective hydrogenation step a), all of the diolefins initially present in the feedstock were converted.

[0224] The effluent 4 obtained from the selective hydrogenation step a) is subjected directly, without separation, to a hydrotreatment step b) performed in a fixed bed in the presence of hydrogen 5 and of a hydrotreatment catalyst of NiMo type on alumina under the conditions presented in Table 4.

TABLE-US-00004 TABLE 4 conditions of the hydrotreatment step b) Hydrotreatment temperature ° C. 355 Partial pressure of hydrogen MPa abs 6.2 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 0.5 volume of catalysts)

[0225] The effluent 6 obtained from the hydrotreatment step b) is subjected directly, without separation, to a first hydrocracking step c) performed in a fixed bed in the presence of hydrogen 7 and of a zeolitic hydrocracking catalyst comprising NiMo under the conditions presented in Table 5.

TABLE-US-00005 TABLE 5 conditions of the first hydrocracking step c) Hydrocracking temperature ° C. 350 Partial pressure of hydrogen MPa abs 5.8 H.sub.2/HC (volume coverage of hydrogen Nm.sup.3/m.sup.3 350 relative to the feedstock volume of step c)) HSV (volume flow rate of feedstock step c)// h.sup.−1 2 volume of catalysts)

[0226] The effluent 8 obtained from the hydrocracking step c) is subjected to a separation step d) according to the invention in which a stream of water is injected into the effluent obtained from the hydrocracking step c); the mixture is then sent into the separation step d) and is treated in a column for washing the acidic gases. A gas fraction 10 is obtained at the top of the acidic gas washing column whereas, at the bottom, a two-phase separating vessel makes it possible to separate an aqueous phase and a liquid phase. The gas washing column and the two-phase separator are operated at high pressure. The liquid phase is then sent into a low-pressure vessel so as to recover a second gas fraction, which is purged, and a liquid effluent. The liquid effluent 12 obtained on conclusion of the separation step d) is sent to a fractionation step e) comprising a stripping column and a distillation column for the purpose of obtaining a fraction with a boiling point of less than or equal to 175° C. (PI−175° C. fraction) and a fraction with a boiling point of greater than 175° C. (175° C.+ fraction).

[0227] The 175° C.+ fraction obtained from the fractionation step e) is sent into the second hydrocracking step f) so as to increase the conversion of compounds with a boiling point of greater than 175° C. A small portion of the 175° C.+ fraction is not sent into the second hydrocracking step f) so as to avoid the accumulation of polyaromatic compounds which could be coke precursors (purge 15b).

[0228] The volume flow rate of 175° C.+ fraction obtained from the fractionation step e) and sent into the second hydrocracking step f) is equal to 80% of the volume flow rate of the liquid effluent obtained from the hydrotreatment step b) and feeding the first hydrocracking step c).

[0229] The second hydrocracking step f) is performed in a fixed bed and in the presence of hydrogen 16 and of a zeolitic hydrocracking catalyst comprising NiMo under the conditions presented in Table 6.

TABLE-US-00006 TABLE 6 conditions of the second hydrocracking step f) Hydrocracking temperature ° C. 320 Partial pressure of hydrogen MPa abs 5.8 H.sub.2/HC (volume coverage of hydrogen Nm.sup.3/m.sup.3 350 relative to the volume of feedstock from step f)) HSV (volume flow rate of feedstock from step f)/ h.sup.−1 2 volume of catalysts)

[0230] The effluent 17 obtained from the second hydrocracking step f) is mixed with the effluent 8 from the first hydrocracking step c). The two effluents are subjected to a separation step d) and then a fractionation step e), these two steps being common to the two effluents and being performed as described above.

[0231] Table 7 gives the overall yields for the various fractions obtained at the outlet of the hydrocracking steps c) and f) on conclusion of the separation step d) and the fractionation step e) (which comprises a stripping column and a distillation column).

TABLE-US-00007 TABLE 7 yields for the various products and fractions obtained at the outlet of the hydrocracking steps c) and f) H.sub.2S* % m/m 0.27 NH.sub.3* % m/m 0.09 C1 % m/m 0.21 C2 % m/m 0.21 C3 % m/m 1.76 C4 % m/m 6.34 PI-175° C. Fraction % m/m 93.00 175° C.+ Fraction % m/m 0.50 Total % m/m 102.37

[0232] 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).

[0233] Treatment of the feedstock according to the steps of the invention, and notably via the hydrocracking steps c) and f), makes it possible to obtain a very high yield of PI−175° C. fraction of naphtha type.

[0234] The characteristics of the liquid fractions PI−175° C. and 17500+ obtained after the separation step d) and a fractionation step e) are presented in Table 8:

TABLE-US-00008 TABLE 8 characteristics of the PI-175° C. and 175° C.+ fractions PI-175° C. Fraction 175° C.+ Fraction Density at 15° C. (ASTM D4052) g/cm.sup.3 0.753 0.805 Content of: Sulfur (ASTM D5453) ppm by weight <2 <2 Nitrogen (ASTM D4629) ppm by weight <0.5 <3 Fe (ASTM D5185) ppb by weight Not detected 25 Total metals (ASTM D5185) ppm by weight Not detected 1 Chlorine (ASTM D7536) ppb by weight Not detected <25 Paraffins (UOP990-11) weight % 82 83 Naphthenes (UOP990-11) weight % 17.5 15 Olefins (UOP990-11) weight % Not detected Not detected Aromatics (UOP990-11) weight % 0.5 1 Simulated distillation (ASTM D2887) in % 0 ° C. 25 175 5 ° C. 38 185 10 ° C. 59 206 30 ° C. 90 235 50 ° C. 118 265 70 ° C. 140 285 90 ° C. 163 320 95 ° C. 175 344 100 ° C. 180 350

[0235] The liquid fractions PI−175° C. and 175° C.+ both have compositions that are compatible with a steam cracking unit, since: [0236] they do not contain any olefins (monoolefins and diolefins); [0237] they have very low contents of chlorine element (respectively, an undetected content and a content of 25 ppb by weight), below the limit required for a steam cracking feedstock; [0238] 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.+ fraction; contents of Fe not detected for the PI−175° C. fraction and of 50 ppb by weight for the 175° C.+ fraction), which are below the limits required for a steam cracking feedstock (≤5.0 ppm by weight, very preferably ≤1 ppm by weight for metals; ≤100 ppb by weight for Fe); [0239] finally, they contain sulfur (<2 ppm by weight for the PI−175° C. fraction and <2 ppm by weight for the 175° C.+ fraction) and nitrogen (<0.5 ppm by weight for the PI−175° C. fraction and <3 ppm by weight for the 175° C.+ fraction) with contents that are very much lower than the limits required for a steam cracking feedstock (s 500 ppm by weight, preferably ≤200 ppm by weight for S and N).

[0240] The liquid fraction PI−175° C. obtained is thus subsequently sent into a steam cracking step h) (cf. Table 9).

TABLE-US-00009 TABLE 9 conditions of the steam cracking step Pressure at furnace exit MPa abs 0.2 Temperature at furnace exit of PI-175° C. fractions ° C. 800 Steam/PI-175° C. fractions ratio kg/kg 0.6 Furnace residence time of PI-175° C. fractions s 0.3

[0241] 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 10 (yield=mass % of product relative to the mass of the PI−175° C. fraction upstream of the steam cracking step, noted as % m/m).

TABLE-US-00010 TABLE 10 yields for the steam cracking step Fraction PI-175° C. Fraction H.sub.2, CO, C1 % m/m 7.9 Ethylene % m/m 34.3 Propylene % m/m 18.7 C4 cut % m/m 14.9 Pyrolysis gasoline % m/m 19.3 Pyrolysis oil % m/m 4.9

[0242] Considering the yield of 93% obtained for the liquid fraction 175° C.+ during the pyrolysis oil treatment process at the outlet of the hydrocracking steps (cf. Table 7), it is possible to determine the overall yields for the products obtained from the steam cracking step i) relative to the initial feedstock of plastics pyrolysis oil type introduced into step a):

TABLE-US-00011 TABLE 11 overall yields for the process of products obtained from the steam cracking step for the PI-175° C. fraction Fraction PI-175° C. Fraction H.sub.2, CO, C1 % m/m 7.4 Ethylene % m/m 31.9 Propylene % m/m 17.4 C4 cut % m/m 13.9 Pyrolysis gasoline % m/m 17.9 Pyrolysis oil % m/m 4.5

[0243] When the PI−175° C. fraction is 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 31.9% and 17.4% relative to the mass amount of initial feedstock of plastics pyrolysis oil type.

[0244] 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 (not in Accordance with the Invention)

[0245] In this example, the feedstock to be treated is identical to that described in Example 1 (cf. Table 2).

[0246] It undergoes the steps a) of selective hydrogenation, b) of hydrotreatment and d) of separation, performed under the same conditions as those described in Example 1. In this example not in accordance with the invention, the effluent obtained from the hydrotreatment step is not subjected to the hydrocracking steps c) and f). The liquid effluent obtained on conclusion of the separation step d) constitutes the PI+ fraction.

[0247] The yields for the various products and for the various fractions obtained at the outlet of the hydrotreatment step b) are indicated in Table 12 (the yields corresponding to the ratios of the mass amounts of the various products obtained relative to the mass of feedstock upstream of step a), expressed in percentages and noted as % m/m).

TABLE-US-00012 TABLE 12 yields for the various products and fractions obtained at the outlet of the hydrotreatment step b) H.sub.2S % m/m 0.27 NH.sub.3 % m/m 0.09 C1 % m/m 0.01 C2 % m/m 0.02 C3 % m/m 0.09 C4 % m/m 0.38 PI+ Fraction 99.55 Total % m/m 100.05

[0248] The characteristics of the PI+ fraction (which corresponds to the liquid effluent) obtained after the separation step d) are presented in Table 13:

TABLE-US-00013 TABLE 13 characteristics of the PI+ fraction PI+ Fraction Density at 15° C. (ASTM D4052) g/cm.sup.3 0.803 Content of: Sulfur (ASTM D5453) ppm by weight <2 Nitrogen (ASTM D4629) ppm by weight <0.8 Fe (ASTM D5185) ppb by weight Not detected Total metals (ASTM D5185) ppm by weight Not detected Chlorine (ASTM D7536) ppb by weight Not detected Paraffins (UOP990-11) weight % 66 Naphthenes (UOP990-11) weight % 32 Olefins (UOP990-11) weight % Not detected Aromatics (UOP990-11) weight % 2 Simulated distillation (ASTM D2887) in % 0 ° C. 26 5 ° C. 55 10 ° C. 93 30 ° C. 157 50 ° C. 226 70 ° C. 304 90 ° C. 390 95 ° C. 397 100 ° C. 431

[0249] The PI+ fraction obtained via the sequence of steps a), b) and d) consists of about 35% of compounds of naphtha type with a boiling point less than or equal to 175° C. This low yield of compounds of naphtha type with a boiling point of less than or equal to 17500 is due to the absence of the hydrocracking steps in this example not in accordance.

[0250] The liquid effluent fraction PI+ is sent directly into a steam cracking step i) under the conditions mentioned in Table 14.

TABLE-US-00014 TABLE 14 conditions of the steam cracking step Pressure at furnace exit MPa abs 0.2 Temperature at furnace exit of PI+ fraction ° C. 795 Steam/PI+ fraction ratio kg/kg 0.7 Furnace residence time of PI+ fraction s 0.3

[0251] The effluent from the steam cracking furnace is subjected to a separation step which enables recycling of the saturated compounds into the steam cracking furnace and the production of the yields indicated in Table 15 (yield=mass % of product relative to the mass of PI+ fraction upstream of the steam cracking step, noted as % m/m).

TABLE-US-00015 TABLE 15 yields for the steam cracking step for the PI+ fraction Fraction PI+ Fraction H.sub.2, CO, C1 % m/m 8.1 Ethylene % m/m 34.8 Propylene % m/m 19.0 C4 cut % m/m 15.1 Pyrolysis gasoline % m/m 18.8 Pyrolysis oil % m/m 4.2

[0252] Considering the yield of 99.5% obtained for the PI+ fraction during the pyrolysis oil treatment process at the outlet of the hydrotreatment step b) (cf. Table 12), it is possible to determine the overall yields for the products obtained from the steam cracking step i) relative to the initial feedstock of plastics pyrolysis oil type introduced into step a):

TABLE-US-00016 TABLE 16 overall yields for the process of products obtained from the steam cracking step for the PI+ fraction Fraction PI+ Fraction H.sub.2, CO, C1 % m/m 8.1 Ethylene % m/m 34.6 Propylene % m/m 18.9 C4 cut % m/m 15.0 Pyrolysis gasoline % m/m 18.7 Pyrolysis oil % m/m 4.2

[0253] When the liquid fraction PI+ is subjected to a steam cracking step, the process according to the invention makes it possible to achieve overall mass yields of ethylene and propylene, respectively, of 34.6% and 18.9% relative to the mass amount of initial feedstock of plastics pyrolysis oil type.