Methods and compositions for chemical recovery of polymers with reduced phosphorus content

Abstract

The present invention relates to a method of chemical recovery, wherein the method comprises the steps of: i. Supplying a composition of a polymer; ii. Subjecting the composition of polymers to a heat treatment to obtain a pyrolysis oil; iii. Optionally, subjecting the product obtained in step ii. To a hydrotreating process; iv. Subjecting the product obtained in step ii. Or the product obtained in step iii. When applied to a thermal decomposition process to obtain a chemical composition comprising ethylene and propylene; wherein in the composition of the polymer, one or more stabilizing compounds comprising phosphorus atoms are present only in an amount such that such one or more stabilizing compounds contribute to at most 100 ppm, preferably at most 50 ppm, more preferably at most 25 ppm, even more preferably at most 10 ppm of phosphorus atoms, relative to the total weight of the composition of the polymer. This process enables efficient chemical recovery of polymers using a simplified process, wherein corrosion of equipment employed in the process is reduced. This process allows the use of an increased proportion of the product of step ii., such as a pyrolysis oil product, and / or the product of step iii., such as a hydrotreated pyrolysis oil product, without detrimental effects on the steam cracking process, such as corrosion, shortening the service life of the steam cracker, or fouling, for example in the operations of chemical recovery including steam cracking.

Description

[0001] The present invention relates to a method for the chemical recycling of polymers. The present invention further relates to a composition of polymers suitable for use in a chemical recycling method, in particular for a chemical recycling method comprising pyrolyzing a polymer composition to obtain pyrolysis oil and subsequently processing such pyrolysis oil via steam cracking or refinery operations to obtain a chemical feed stream for the production of polymers.

[0002] To alleviate the end-of-life issues regarding polymeric materials, such as thermoplastics, there is an increasingly stringent drive to seek applications where polymeric materials that are no longer considered useful for their original use can be meaningfully utilized while minimizing the environmental burden, such as by landfilling waste materials or incineration.

[0003] To achieve such applications, a large number of material recycling solutions have been and are being investigated. As part of such research, a particularly important specific aspect to consider is the chemical composition of the polymeric materials available for processing. Generally, because of the fact that available polymeric material streams are typically collected in a combined manner, such streams contain various polymers with different chemical compositions; at the user level, for example in households, the knowledge and means to allow a user to separate one type of polymer from others are generally not available and cannot be expected. And although certain plastic sorting techniques are available and are increasingly developed, the current situation is that in practice the vast majority of waste plastic streams contain polymeric materials with different chemical properties, and it is foreseeable that this situation will not change.

[0004] Therefore, it is recognized that compositions of waste polymers with different chemical properties can be processed via routes with a desired high value and a desired low environmental impact.

[0005] One specific route for processing mixed streams of waste polymers that has gained acceptance is via a chemical recycling route. Such routes generally include the following stages: the first stage is to process a waste polymer stream with a certain defined composition to produce one or more chemical compositions with an oily nature, such as a composition comparable to a naphtha-type composition obtainable from refined fossil crude oil, and this stage can then be followed by processing such oily compositions via a thermochemical decomposition method to obtain a hydrocarbon chemical composition containing a range of chemicals, which can be used again to manufacture new or 'original' products including 'original' polymeric materials such as polyethylene and polypropylene.

[0006] Such chemical recycling routes can be considered as part of a solution for dealing with the abundantly available waste plastic streams. However, the composition of the waste plastic streams can affect the operating efficiency of such chemical recycling routes.

[0007] A particular element that can be detrimental to the ability to process waste plastics via a chemical recycling route is phosphorus. The presence of phosphorus can lead to equipment corrosion and catalyst poisoning in unit operations used to produce chemical compositions containing ethylene and propylene, such as in steam cracking operations.

[0008] To mitigate this problem, methods in the art provide separation unit operations for trapping phosphorus-containing compounds at various stages of the chemical recycling process. Such stages can include a hydrotreating stage and a refining stage. As will be understood, in view of process efficiency, it is preferred to minimize the additional stages required in such a chemical recycling process; each stage has a cost, involves additional energy consumption, and results in a reduced process yield. Accordingly, it is desirable to employ methods that must incorporate the fewest possible unit operations or process stages.

[0009] The inventors of the present application have now discovered a particularly suitable chemical recycling method, wherein the method comprises the following steps:

[0010] i. Supplying a composition of polymers;

[0011] ii. Subjecting the composition of polymers to a heat treatment to obtain pyrolysis oil;

[0012] iii. Optionally, subjecting the product obtained in step ii. to a hydrotreating process;

[0013] iv. Subjecting the product obtained in step ii. or the product obtained in step iii. when applied to a thermal decomposition process to obtain a chemical composition containing ethylene and propylene;

[0014] wherein, in the composition of polymers, one or more stabilizing compounds containing phosphorus atoms are present only in such an amount that such one or more stabilizing compounds contribute at most 100 ppm, preferably at most 50 ppm, more preferably at most 25 ppm, and even more preferably at most 10 ppm of phosphorus atoms relative to the total weight of the composition of polymers.

[0015] This method can effectively chemically recycle polymers using a simplified process, wherein corrosion of the equipment employed in the method is reduced. For example, in an operation where chemical recycling includes steam cracking, this method allows the use of an increased proportion of the product of step ii., such as the pyrolysis oil product, and / or the product of step iii., such as the hydrotreated pyrolysis oil product, without detrimental effects on the steam cracking process, such as corrosion, shortening the service life of the steam cracker, or fouling.

[0016] For example, one or more stabilization compounds may contain only such an amount of oxygen atoms that such one or more stabilization compounds contribute up to 150 ppm, preferably up to 100 ppm, more preferably up to 50 ppm, even more preferably up to 25 ppm of oxygen atoms based on the total weight of the composition of the polymer.

[0017] The composition of the polymer may, for example, comprise one or more stabilization compounds, wherein the one or more stabilization compounds are compounds comprising one or more structural moieties according to formula I:

[0018]

[0019] Preferably, the one or more stabilization compounds are selected from triphenyl phosphite, triphenyl phosphate, tris(2,4-di-tert-butylphenyl) phosphite, tris(2,4-di-tert-butylphenyl) phosphate, bisphenol A bis(diphenyl phosphate), bisphenol A phosphite, resorcinol bis(diphenyl phosphate), resorcinol bis(di-2,6-xylyl phosphate), triphenyl thiophosphate, tris(2-methylphenyl) phosphite, tris(2-methylphenyl) phosphate, tris(3-methylphenyl) phosphite, tris(3-methylphenyl) phosphate, tris(4-methylphenyl) phosphite, tris(4-methylphenyl) phosphate, tris(4-tert-butylphenyl) phosphate, tris(4-tert-butylphenyl) phosphite, tris(4-nonylphenyl) phosphite, hydroquinone bis(diphenyl phosphate), bis[2,4-bis(1,1-dimethylpropyl)phenyl][4-(1,1-dimethylpropyl)phenyl] phosphite, bis[4-(1,1,-dimethylpropyl)phenyl][2,4-bis(1,1-dimethylpropyl)phenyl] phosphite, tris[2,4-bis(1,1,-dimethylpropyl)phenyl] phosphite, and tris[4-(1,1,-dimethylpropyl)phenyl] phosphite.

[0020] For example, the composition of the polymer may comprise one or more stabilization compounds in an amount of ≤ 5000 ppm by weight, preferably ≥ 500 and ≤ 5000 ppm by weight, more preferably ≥ 500 and ≤ 3000 ppm by weight based on the total weight of the composition of the polymer.

[0021] Preferably, the composition of the polymer comprises ≥ 1 ppb by weight, preferably ≥ 5 ppb by weight, more preferably ≥ 10 ppb by weight of phosphorus atoms based on the total weight of the composition of the polymer.

[0022] Preferably, the composition of the polymer comprises ≥ 1 ppb by weight, preferably ≥ 5 ppb by weight, more preferably ≥ 10 ppb by weight of oxygen atoms based on the total weight of the composition of the polymer.

[0023] Preferably, the polymer composition contains phosphorus atoms in an amount of ≥1 ppb by weight, preferably ≥5 ppb, more preferably ≥10 ppb, based on the total weight of the polymer composition, and oxygen atoms in an amount of ≥1 ppb by weight, preferably ≥5 ppb, more preferably ≥10 ppb, based on the total weight of the polymer composition.

[0024] The heat treatment in step ii may include, for example, a mild pyrolysis process, where the pyrolysis of the polymer composition is carried out at a temperature of ≥250 °C and ≤450 °C; or a severe pyrolysis process, where the pyrolysis of the polymer composition is carried out at a temperature of >450 °C and ≤650 °C.

[0025] Alternatively, the heat treatment may be a catalytic process, preferably a process where the heat treatment is carried out in the presence of a ZSM-5 zeolite catalyst and / or a spent FCC catalyst.

[0026] In the method of the present invention, the hydrotreating step iii may be carried out in the presence of hydrogen, at a temperature of ≤350 °C, preferably at a pressure of ≤10.0 MPa, preferably ≥1.0 and ≤10.0 MPa, more preferably ≥2.0 and ≤7.0 MPa.

[0027] For example, the hydrotreating step iii may be carried out in the presence of a catalyst selected from: a cobalt-molybdenum catalyst on an alumina support, a nickel-molybdenum catalyst on an alumina support, a tungsten-molybdenum catalyst on an alumina support, a platinum-palladium catalyst on an alumina support, a nickel sulfide catalyst, a molybdenum sulfide catalyst, or a nickel-molybdenum sulfide catalyst.

[0028] The thermal decomposition process in step iv may be a steam cracking process, preferably where the steam cracking occurs in a steam cracking unit containing heating coils, where the coil outlet temperature (COT) is 800 °C to 870 °C. Alternatively, the thermal decomposition process in step iv may be a catalytic cracking process.

[0029] In an embodiment where the thermal decomposition process in step iv is a steam cracking process, the feed composition supplied to the steam cracking process may, for example, contain ≥2.5 wt% and ≤75.0 wt%, preferably ≥5.0 wt% and ≤50.0 wt%, more preferably ≥10.0 wt% and ≤50.0 wt% of the product obtained in step ii.

[0030] Alternatively, the feed composition supplied to the steam cracking process may, for example, contain ≥2.5 wt% and ≤75.0 wt%, preferably ≥5.0 wt% and ≤50.0 wt%, more preferably ≥10.0 wt% and ≤50.0 wt% of the product obtained in step iii.

[0031] In the process of the present invention, the polymer composition may for example comprise, based on the total weight of the polymer composition:

[0032] · ≥ 70.0% by weight of a polyolefin composition;

[0033] · at most 50 ppm, preferably ≥ 1 ppb and ≤ 25 ppm of phosphorus atoms; and

[0034] · preferably at most 100 ppm, more preferably ≥ 1 ppb and ≤ 50 ppm of oxygen atoms;

[0035] Preferably, the composition is obtained as a waste plastic stream from post - consumer waste.

[0036] The present invention also relates to a polymer composition comprising, based on the total weight of the polymer composition:

[0037] · ≥ 70.0% by weight of a polyolefin composition;

[0038] · ≥ 0.1 and ≤ 20.0% by weight of a polyester composition;

[0039] · ≥ 0.1 and ≤ 20% by weight of a polyamide composition; and

[0040] · one or more stabilizing compounds comprising phosphorus atoms, the amount of the one or more stabilizing compounds being such that the one or more stabilizing compounds contribute at most 50 ppm of phosphorus atoms, and the one or more stabilizing compounds preferably comprising such an amount of oxygen atoms that the one or more stabilizing compounds contribute at most 100 ppm of oxygen atoms;

[0041] Preferably, the composition is obtained as a waste plastic stream from post - consumer waste.

[0042] The polymer composition may for example comprise one or more stabilizing compounds, wherein the one or more stabilizing compounds are compounds comprising one or more structural moieties according to formula I:

[0043]

[0044] Particularly preferably, the polymer composition is obtained as a waste plastic stream, for example a waste plastic stream from post - consumer or household waste.

[0045] The present invention also relates to the use of the polymer composition according to the present invention for reducing fouling and / or corrosion in a steam cracking process of a chemical feed of a material comprising a waste plastic source.

[0046] This process can effectively chemically recycle polymers using a simplified process, in which the corrosion of the equipment used in the process is reduced.

[0047] The hydrotreating process of step iii. can be carried out, for example, in one or more containers configured to accommodate a hydrotreating catalyst. The containers can be configured to operate in a gas phase, a liquid phase, a vapor-liquid phase, or a slurry phase. The containers can include one or more beds of the hydrotreating catalyst. Such one or more beds can be one or more fixed beds, one or more fluidized beds, one or more moving beds, one or more slurry beds, or a combination thereof. The containers can be operated under adiabatic, isothermal, non-adiabatic, or non-isothermal conditions.

[0048] In the hydrotreating step, the product of step ii. can be subjected to treatment in the presence of hydrogen, where the volume flow rate ratio of hydrogen to the product of step ii. can be, for example, from 10 to 3000, preferably from 200 to 1000.

[0049] The hydrotreating step iii. can be carried out in the presence of a catalyst. Such a catalyst can be, for example, a catalyst selected from: a cobalt-molybdenum catalyst on an alumina support, a nickel-molybdenum catalyst on an alumina support, a tungsten-molybdenum catalyst on an alumina support, a platinum-palladium catalyst on an alumina support, a nickel sulfide catalyst, a molybdenum sulfide catalyst, or a nickel-molybdenum sulfide catalyst.

[0050] The catalyst that can be used in the hydrotreating step iii. can be, for example, sulfided.

[0051] The composition of the polymer preferably contains ≥70.0% by weight of polyolefins. Such polyolefins preferably contain polyethylene and polypropylene. Specifically, the polyolefins can contain ≥80.0% by weight of polyethylene or ≥90.0% by weight of polyethylene. The polyolefins can contain ≤20.0% by weight of polypropylene or ≤10.0% by weight of polypropylene.

[0052] Such polyethylene can be a composition containing low-density polyethylene, linear low-density polyethylene, and high-density polyethylene.

[0053] Particularly preferably, the composition of the polymer contains a high proportion of polyolefins, such as ≥70.0% by weight or ≥80.0% by weight or ≥90.0% by weight relative to the total weight of the composition of the polymer. Due to the fact that the polymer structure of the composition of the polymer containing such a high proportion of polyolefins is based on linear monomers suitable for thermal cracking, such a composition of the polymer is particularly suitable for chemical recycling via a catalytic or non-catalytic heat treatment process.

[0054] Via such thermal cracking, such as steam cracking or catalytic cracking, a composition of plastics, particularly a composition of waste plastics, can be converted into chemical structural units, specifically ethylene and propylene.

[0055] Therefore, the method of the present invention allows for the suitable conversion of waste plastics into new plastics with high quality, thereby creating a circular economy for material use.

Claims

1. A method for the chemical recycling of a polymer, the method comprising the steps of: i. Supplying a composition of the polymer; ii. Subjecting the composition of the polymer to a heat treatment to obtain pyrolysis oil; iii. Optionally, subjecting the product obtained in step ii. to a hydrotreating process; iv. Subjecting the product obtained in step ii. or the product obtained in step iii. when applied to a thermal decomposition process to obtain a chemical composition comprising ethylene and propylene; wherein, in the composition of the polymer, one or more stabilizing compounds containing phosphorus atoms are present only in such an amount that such one or more stabilizing compounds contribute at most 100 ppm, preferably at most 50 ppm, more preferably at most 25 ppm, even more preferably at most 10 ppm of phosphorus atoms relative to the total weight of the composition of the polymer.

2. The method according to claim 1, wherein the one or more stabilizing compounds contain only such an amount of oxygen atoms that such one or more stabilizing compounds contribute at most 150 ppm, preferably at most 100 ppm, more preferably at most 50 ppm, even more preferably at most 25 ppm of oxygen atoms relative to the total weight of the composition of the polymer.

3. The method according to any one of claims 1-2, wherein the one or more stabilizing compounds are compounds containing one or more structural moieties according to formula I:

4. The method according to any one of claims 1-3, wherein the one or more stabilizing compounds are selected from triphenyl phosphite, triphenyl phosphate, tris(2,4-di-tert-butylphenyl) phosphite, tris(2,4-di-tert-butylphenyl) phosphate, bisphenol A bis(diphenyl phosphate), bisphenol A phosphite, resorcinol bis(diphenyl phosphate), resorcinol bis(di-2,6-xylyl phosphate), triphenyl thiophosphate, tris(2-methylphenyl) phosphite, tris(2-methylphenyl) phosphate, tris(3-methylphenyl) phosphite, tris(3-methylphenyl) phosphate, tris(4-methylphenyl) phosphite, tris(4-methylphenyl) phosphate, tris(4-tert-butylphenyl) phosphate, tris(4-tert-butylphenyl) phosphite, tris(4-nonylphenyl) phosphite, hydroquinone bis(diphenyl phosphate), bis[2,4-bis(1,1-dimethylpropyl)phenyl][4-(1,1-dimethylpropyl)phenyl] phosphite, bis[4-(1,1,-dimethylpropyl)phenyl][2,4-bis(1,1-dimethylpropyl)phenyl] phosphite, tris[2,4-bis(1,1,-dimethylpropyl)phenyl] phosphite, and tris[4-(1,1,-dimethylpropyl)phenyl] phosphite.

5. The method according to any one of claims 1-4, wherein the composition of the polymer comprises ≥1 ppb by weight, preferably ≥5 ppb by weight, more preferably ≥10 ppb by weight of phosphorus atoms, and preferably wherein the composition of the polymer comprises ≥1 ppb by weight, preferably ≥5 ppb by weight, more preferably ≥10 ppb by weight of oxygen atoms, based on the total weight of the composition of the polymer.

6. The method according to any one of claims 1-5, wherein the heat treatment in step ii. comprises a mild pyrolysis process, wherein the pyrolysis of the composition of the polymer is carried out at a temperature of ≥250 °C and ≤450 °C; or a severe pyrolysis process, wherein the pyrolysis of the composition of the polymer is carried out at a temperature of >450 °C and ≤650 °C.

7. The method according to any one of claims 1-6, wherein the heat treatment is a catalytic process, preferably wherein the heat treatment is a process operated in the presence of a ZSM-5 zeolite catalyst and / or a spent FCC catalyst.

8. The method according to any one of claims 1-7, wherein the hydrotreating step iii. is carried out in the presence of hydrogen at a temperature of ≤350 °C, preferably at a pressure of ≤10.0 MPa, preferably ≥1.0 and ≤10.0 MPa, more preferably ≥2.0 and ≤7.0 MPa.

9. The method according to any one of claims 1-8, wherein the hydrotreating step iii. is carried out in the presence of a catalyst selected from: a cobalt-molybdenum catalyst on an alumina support, a nickel-molybdenum catalyst on an alumina support, a tungsten-molybdenum catalyst on an alumina support, a platinum-palladium catalyst on an alumina support, a nickel sulfide catalyst, a molybdenum sulfide catalyst, or a nickel-molybdenum sulfide catalyst.

10. The method according to any one of claims 1-9, wherein the thermal decomposition process in step iv. is a steam cracking process, preferably wherein the steam cracking occurs in a steam cracking unit comprising heating coils, wherein the coil outlet temperature (COT) is 800 °C to 870 °C; or wherein the thermal decomposition process in step iv. is a catalytic cracking process.

11. The method according to claim 10, wherein the feed composition supplied to the steam cracking process comprises ≥2.5 wt% and ≤75.0 wt%, preferably ≥5.0 wt% and ≤50.0 wt%, more preferably ≥10.0 wt% and ≤50.0 wt% of the product obtained in step ii.; and / or wherein the feed composition supplied to the steam cracking process comprises ≥2.5 wt% and ≤75.0 wt%, preferably ≥5.0 wt% and ≤50.0 wt%, more preferably ≥10.0 wt% and ≤50.0 wt% of the product obtained in step iii.

12. The method according to any one of claims 1-11, wherein the composition of the polymer comprises, based on the total weight of the composition of the polymer: ● ≥70.0 wt% of a polyolefin composition; ● at most 50 ppm, preferably ≥1 ppb and ≤25 ppm of phosphorus atoms; and ● Preferably, oxygen atoms are at most 100 ppm, more preferably ≥ 1 ppb and ≤ 50 ppm; Preferably, the composition is obtained as a waste plastic stream from post-consumer waste.

13. A composition of polymers, comprising, based on the total weight of the composition of polymers: ● ≥ 70.0 wt% of a polyolefin composition; ● ≥ 0.1 and ≤ 20.0 wt% of a polyester composition; ● ≥ 0.1 and ≤ 20 wt% of a polyamide composition; and ● One or more stabilizing compounds comprising phosphorus atoms, the amount of the one or more stabilizing compounds being such that the one or more stabilizing compounds contribute at most 50 ppm of phosphorus atoms, and the one or more stabilizing compounds preferably comprise such an amount of oxygen atoms that the one or more stabilizing compounds contribute at most 100 ppm of oxygen atoms; Preferably, the composition is obtained as a waste plastic stream from post-consumer waste.

14. The composition according to claim 13, wherein the one or more stabilizing compounds are compounds comprising one or more structural moieties according to formula I:

15. Use of the composition of polymers according to any one of claims 13 - 14 for reducing fouling and / or corrosion in the steam cracking process of a chemical feedstock comprising a waste plastic source.

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