METHOD FOR PROCESSING PLASTIC PYROLYSIS OILS WITH A VIEW TO THEIR USE IN A STEAM-CRACKING UNIT

Abstract

A process for treating a plastics pyrolysis oil: a) selective hydrogenation of feedstock in the presence of hydrogen and at least one selective hydrogenation catalyst, at 100 to 150° C., a partial pressure of hydrogen of 1.0 to 10.0 MPa abs. and an hourly space velocity of 1.0 to 10.0 h.sup.−1, to obtain a hydrogenated effluent; b) hydrotreatment of hydrogenated effluent in the presence of hydrogen and at least one hydrotreatment catalyst, at 250 to 370° C., a partial pressure of hydrogen of 1.0 to 10.0 MPa abs. and an hourly space velocity of 1.0 to 10.0 h.sup.−1, to obtain a hydrotreatment effluent; c) separation of hydrotreatment effluent obtained from b) in the presence of an aqueous stream, at a temperature of 50 to 370° C., to obtain at least one gaseous effluent, an aqueous liquid effluent and a hydrocarbon liquid effluent.

Claims

1. A process for treating a feedstock comprising a plastics pyrolysis oil, comprising at least the following steps: a) a selective hydrogenation step performed in a reaction section fed with said feedstock and a gaseous stream comprising hydrogen, in the presence of at least one selective hydrogenation catalyst, at a temperature of between 100 and 250° C., a partial pressure of hydrogen of between 1.0 and 10.0 MPa abs. and an hourly space velocity of between 1.0 and 10.0 h.sup.−1, to obtain a hydrogenated effluent; b) a hydrotreatment step performed in a hydrotreatment reaction section, comprising a fixed-bed reactor containing n catalytic beds, n being an integer greater than or equal to 1, placed in series and each comprising at least one hydrotreatment catalyst, said hydrotreatment reaction section being fed, at the first catalytic bed, with said hydrogenated effluent obtained from step a) and a gaseous stream comprising hydrogen and 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 separation step, fed with the hydrotreatment effluent obtained from step b) 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 effluent.

2. The process as claimed in claim 1, comprising a step a.sub.0) of pretreating the feedstock comprising a plastics pyrolysis oil, said pretreatment step being performed prior to the selective hydrogenation step a) in an adsorption section fed with said feedstock and operating at a temperature of between 0 and 150° C., preferably between 5 and 100° C., and at a pressure of between 0.15 and 10.0 MPa abs., preferably between 0.2 and 1.0 MPa abs., in the presence of at least an adsorbent having a specific surface area of greater than or equal to 100 m.sup.2/g, preferably greater than or equal to 200 m.sup.2/g, to obtain a pretreated feedstock which feeds the mixing section of step a).

3. The process as claimed in claim 1, wherein the selective hydrogenation step a) is performed at a temperature of between 110 and 200° C., preferably between 130 and 180° C., in step a).

4. The process as claimed in claim 1, wherein the amount of the gaseous stream feeding the reaction section of step a) is such that the hydrogen coverage is between 1 and 50 Nm.sup.3 of hydrogen per m.sup.3 of feedstock, and preferably between 5 and 20 Nm.sup.3 of hydrogen per m.sup.3 of feedstock.

5. The process as claimed in claim 1, wherein the reaction section of step a) uses at least two reactors operating in a permutable system.

6. The process as claimed in claim 1, wherein said at least selective hydrogenation catalyst comprises a support, preferably 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, preferably chosen from the group consisting of nickel and cobalt, and/or at least one group VIB element, preferably chosen from the group consisting of molybdenum and tungsten.

7. The process as claimed in claim 6, wherein said at least one selective hydrogenation catalyst comprises less than 1% by weight of nickel, expressed as nickel oxide NiO, relative to the weight of said catalyst, and less than 5% by weight of molybdenum, expressed as molybdenum oxide MoO.sub.3, relative to the weight of said catalyst, on an alumina support.

8. The process as claimed in claim 1, wherein an additional gaseous stream comprising hydrogen is introduced at the inlet of each catalytic bed from the second catalytic bed, of the hydrotreatment reaction section of step b).

9. The process as claimed in claim 1, wherein the amount of the gaseous stream feeding the hydrotreatment reaction section of step b) is such that the hydrogen coverage is between 50 and 500 Nm.sup.3 of hydrogen per m.sup.3 of hydrogenated effluent obtained from step a), preferably between 50 and 500 Nm.sup.3 of hydrogen per m.sup.3 of hydrogenated effluent obtained from step a), preferably between 100 and 300 Nm.sup.3 of hydrogen per m.sup.3 of hydrogenated effluent obtained from step a).

10. The process as claimed in claim 1, wherein said at least one hydrotreatment catalyst comprises a support, preferably 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, preferably chosen from the group consisting of nickel and cobalt, and/or at least one group VIB element, preferably chosen from the group consisting of molybdenum and tungsten.

11. The process as claimed in claim 1, wherein said at least one hydrotreatment catalyst has a specific surface area of greater than or equal to 250 m.sup.2/g, preferably greater than or equal to 300 m.sup.2/g.

12. The process as claimed in claim 1, also comprising a fractionation step d).

13. The process as claimed in claim 1, also comprising a steam cracking step e), 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.

Description

LIST OF FIGURES

[0087] The information regarding the elements referenced in FIGS. 1 to 3 enables a better understanding of the invention, without said invention being limited to the particular embodiments illustrated in FIGS. 1 to 3. The various embodiments presented may be used alone or in combination with each other, without any limitation to the combination.

[0088] FIG. 1 represents the scheme of one embodiment of the process of the present invention, comprising: [0089] a step a) of selective hydrogenation of a hydrocarbon 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; [0090] 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; [0091] 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.

[0092] 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 separation step c), or else not to inject it, depending on the characteristics of the feedstock.

[0093] FIG. 2 is a variant of the implementation of the process according to the invention represented in FIG. 1. In the embodiment shown in FIG. 2, the hydrocarbon liquid fraction 10, obtained at the end of step c), is sent to a fractionation step d) making it possible to obtain at least one gaseous fraction 11, a fraction comprising naphtha 12 and a hydrocarbon fraction 13.

[0094] FIG. 3 is a variant of the implementation of the process according to the invention represented in FIG. 2. In the embodiment shown in FIG. 3, the hydrocarbon feedstock obtained from the pyrolysis of plastics 1 undergoes a step pretreatment a.sub.0), prior to the selective hydrogenation step a). The feedstock then pretreated 14 feeds the selective hydrogenation step a).

[0095] Only the main steps, with the main streams, are shown in FIGS. 1 to 3, 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 gaseous 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 for recycling hydrogen may also be used.

[0096] At the end of step d), the fraction comprising naphtha 12 and/or the hydrocarbon fraction 13 is/are sent to a steam cracking process.

EXAMPLES

Example 1 (in Accordance with the Invention)

[0097] The feedstock 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 Volume mass @ 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 mgKOH/g 1.5 Bromine content ASTM D1159 g/100 g 80 Diolefin content from the Maleic MAV Method.sup.(1) % by weight 10 Anhydride number Oxygen-bearing compound content Combustion + % by weight 1.0 Infrared Paraffin content UOP990-11 % by weight 45 Naphthene content UOP990-11 % by weight 20 Olefin content UOP990-11 % by weight 25 Aromatic compound content UOP990-11 % by weight 10 Halogen content ASTM-D7359 ppm by weight 350 Asphaltene content IFP9313 ppm by weight 380 Chlorine content ASTM D7536 ppm by weight 320 Metal content: P ASTM-D5185 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:  0% ASTM D2887 ° C. 40  10% ° C. 98  30% ° C. 161  50% ° C. 232  70% ° C. 309  90% ° C. 394 100% ° C. 432 .sup.(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, pp. 57-68

[0098] 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 the 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. 150 Partial pressure of hydrogen MPa abs 6.4 H.sub.2/HC (volume coverage of hydrogen Nm.sup.3/m.sup.3 10 relative to the feedstock volume) HSV (volume flow rate of feedstock/ h.sup.−1 6 volume of catalysts)

[0099] On conclusion of the selective hydrogenation step a), all of the diolefins initially present in the feedstock were converted.

[0100] 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)

[0101] The effluent 6 obtained from the hydrotreatment step b) is subjected to a separation step c): a stream of water is injected into the effluent obtained from the hydrotreatment step b); the mixture is then treated in an acid gas washing column and separating vessels. The liquid effluent obtained is then sent to a fractionation step d) which comprises a stripping column. The yields for the various fractions obtained after separation and fractionation are indicated in table 5 (the yields being 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 percentage and noted as % m/m).

TABLE-US-00005 TABLE 5 yields of the various products obtained after separation and fractionation NH.sub.3 + H.sub.2S % m/m 0.35 C1-C4 Fraction % m/m 0.50 PI− 150° C. Fraction % m/m 28.10 150° C.+ Fraction % m/m 71.40 PI+ Fraction % m/m 99.50

[0102] The characteristics of the PI-150° C. and 150° C.+ liquid fractions (and also the PI+ fraction which is the sum of the PI-150° C. and 150° C.+ fractions) obtained after the separation step c) and a fractionation step are presented in table 6:

TABLE-US-00006 TABLE 6 characteristics of the PI− 150° C, 150° C.+ and PI+ fractions Fraction Fraction Fraction Analysis (method) PI− 150° C. 150° C.+ PI+ Volume mass @ 15° C. g/cm.sup.3 0.750 0.827 0.804 (ASTM D4052) Content of: Sulfur (ASTM D5453) ppm by weight <2 <10 <10 Nitrogen (ASTM D4629) ppm by weight <0.5 <5 <5 Fe (ASTM D5185) ppb by weight Not <50 <50 detected Total metals (ASTM D5185) ppm by weight Not <1 <1 detected Chlorine (ASTM D7536) ppb by weight Not <25 <25 detected Paraffins (UOP990-11) % by weight 68 65 66 Naphthenes (UOP990-11) % by weight 30.5 33 32 Olefins (UOP990-11) % by weight not not not detected detected detected Aromatic compounds (UOP990-11) % by weight 1.5 2 2 Simulated Distillation (ASTM D2887)  0% ° C. 25 150 25  5% ° C. 32 162 53  10% ° C. 40 174 92  30% ° C. 82 226 155  50% ° C. 108 281 227  70% ° C. 126 346 305  90% ° C. 142 395 391  95% ° C. 146 404 398 100% ° C. 150 432 432
The liquid fractions PI-150° C. and 150° C.+ both have compositions that are compatible with a steam cracking unit, since: [0103] they do not contain any olefins (monoolefins and diolefins); [0104] 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 (≤50 ppb by weight); [0105] 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 15000+ fraction; contents of Fe not detected for the PI150° C. fraction and of 50 ppb by weight for the 150° 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); [0106] finally, they contain sulfur (<2 ppm by weight for the PI-150° C. fraction and <10 ppm by weight for the 150° C.+ fraction) and nitrogen (<0.5 ppm by weight for the PI150° C. fraction and <5 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).

[0107] It also appears that the mixture of the two liquid fractions, named PI+, also has very low contents of olefins and of contaminants (in particular of metals, chlorine, sulfur, nitrogen) making the composition compatible with a steam cracking unit.

[0108] The liquid fractions PI-150° C. and 150° C.+ obtained are thus then sent into a steam cracking step where the liquid fractions are cracked under various conditions (cf. Table 7). The PI+ mixture can also be sent directly into a steam cracking step under the conditions mentioned in table 7.

TABLE-US-00007 TABLE 7 conditions of the steam cracking step Pressure at furnace exit MPa abs 0.2 Temperature at furnace exit of PI− 150° C. fractions ° C. 800 Temperature at furnace exit of 150° C.+ fraction ° C. 790 Temperature at furnace exit of PI+ fractions ° C. 795 Steam fraction/PI− 150° C.+ fraction ratio kg/kg 0.6 Steam/150° C.+ fraction ratio kg/kg 0.8 Steam/PI+ fractions ratio kg/kg 0.7 Furnace residence time of PI− 150° C. fractions s 0.3 Furnace residence time of 150° C.+ fractions s 0.3 Furnace residence time of PI+ fractions s 0.3

[0109] 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 8 (yield=mass % of product relative to the mass of each of the fractions upstream of the steam cracking step, noted as % m/m).

TABLE-US-00008 TABLE 8 Yields of the steam cracking step PI− 150° C. 150° C.+ PI+ Fractions Fraction Fraction Fraction H2, CO, C1 % m/m 7.8 7.9 8.1 Ethylene % m/m 33.7 34.2 34.8 Propylene % m/m 18.3 18.6 19.0 C4 cut % m/m 14.6 14.8 15.1 Pyrolysis gasoline % m/m 19.8 19.4 18.8 Pyrolysis oil % m/m 5.7 5.1 4.2

[0110] By considering the yields obtained for the various liquid fractions PI-150° C. and 150° C.+(and their PI+ mixture) during the pyrolysis oil treatment process (see table 5), it is possible to determine the overall yields for the products obtained from the steam cracking step relative to the initial feedstock of plastics pyrolysis oil type introduced into step a):

TABLE-US-00009 TABLE 9 overall yields for the process followed by the steam cracking step PI− 150° C. 150° C.+ PI+ Fractions Fraction Fraction Fraction H2, CO, C1 % m/m 2.2 5.6 8.0 Ethylene % m/m 9.5 24.4 34.7 Propylene % m/m 5.2 13.3 18.9 C4 cut % m/m 4.1 10.6 15.1 Pyrolysis gasoline % m/m 5.6 13.9 18.7 Pyrolysis oil % m/m 1.6 3.6 4.2

[0111] 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 34.7% and 18.9% relative to the mass amount of initial feedstock of plastics pyrolysis oil type. When the PI-150° C. and 150° C.+ fractions are sent separately 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 33.9% (=9.5+24.4) and 18.5% (=5.2+13.3) relative to the mass amount of initial feedstock of plastics pyrolysis oil type.

[0112] 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.

[0113] Example 2 (in accordance with the invention) In this example, the fractionation step includes, in addition to a stripping column, a distillation section so as to obtain a diesel cut that can be integrated directly into a diesel pool, that is to say that meets the specifications required for a diesel and in particular the specification of T90 D86 at 360° C.

[0114] The feedstock to be treated is identical to that described in example 1 (cf. table 2).

[0115] It undergoes the steps a) of selective hydrogenation, b) of hydrotreatment and c) of separation, performed under the same conditions as those described in example 1. The liquid effluent obtained at the end of the separation step c) is sent to a stripping column, as in example 1. At the end of the stripping column, the two fractions PI-150° C. and 150° C.+ are obtained, as in example 1. They have the same characteristics as those of example 1 (cf. table 6). The 150° C.+ fraction is sent to a distillation column where it is distilled into two cuts: a 150-385° C. cut and a 385° C.+ cut. Table 10 gives the overall yields for the various fractions obtained on conclusion of the separation step c) and the fractionation step d) (which comprises a stripping column and a distillation column).

TABLE-US-00010 TABLE 10 yields of the various products obtained after separation and fractionation NH.sub.3 + H.sub.2S % m/m 0.35 Fraction C1-C4 % m/m 0.50 Fraction PI− 150° C. % m/m 28.10 Fraction 150_385° C.+ % m/m 60.90 Fraction 385° C+ % m/m 14.63

[0116] Table 11 gives the characteristics of the 150-385° C. and 385° C.+ cuts, and the EN-590 commercial specifications of a diesel.

TABLE-US-00011 TABLE 11 characteristics of the 150-385° C and 385° C+ cuts, and EN-590 commercial specifications Cut 150- Cut Specifications Characteristics Units 385° C. 385° C.+ EN-590 Volume mass @ 15° C. g/cm.sup.3 0.824 0.844 0.820-0.845 Content of: Sulfur ppm by weight <10 <10 <10 Nitrogen ppm by weight <5 <5 Cetane number D613 55.4 — >51 Cetane index D4737A 54.4 — >46 Aromatic % by weight 2 2 <11 Simulated distillation D2887  0 ° C. 152 377  5 ° C. 160 381  10 ° C. 171 383  30 ° C. 216 391  50 ° C. 263 398  70 ° C. 318 404  90 ° C. 369 420  95 ° C. 380 426 100 ° C. 390 429 Distillation D86  0 ° C. 181 402  5 ° C. 187 403  10 ° C. 193 396  30 ° C. 225 389  50 ° C. 262 384  70 ° C. 305 387  90 ° C. 344 394  95 ° C. 355 398 <360° C. 100 ° C. 358 395

[0117] Table 11 shows that the 150-385° C. cut has the qualities required to be sent directly to the diesel pool.

Example 3 (not in Accordance with the Invention)

[0118] In this example, the hydrocarbon feedstock of pyrolysis oil type identical to that used in example 1 is sent directly to a steam cracking step.

[0119] The yields by mass of the various products obtained are calculated with respect to the initial feedstock (see table 12)

TABLE-US-00012 TABLE 12 Yields of the steam cracking step H2, CO, C1 % m/m 7.7 Ethylene % m/m 33.1 Propylene % m/m 18.0 C4 cut % m/m 14.4 Pyrolysis gasoline % m/m 20.3 Pyrolysis oil % m/m 6.5

[0120] The yields of ethylene and propylene, obtained after direct steam cracking of the pyrolysis oil (process not in accordance with the invention) and presented in table 12, are lower than those obtained after steam cracking of a feedstock obtained from the treatment according to the process of the invention of the same plastics pyrolysis oil of example 1 (cf. table 8), which demonstrates the advantage of the process according to the invention. Additionally, the treatment of pyrolysis oil directly in a steam cracking furnace (example 2) resulted in increased coke formation requiring premature furnace shutdown.