Methods and compositions for chemical recovery of polymers with reduced chlorine 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 the composition of the polymer comprises up to 10 ppm by weight of chlorine atoms relative to the total weight of the composition of the polymer; wherein the composition of the polymer comprises a polyolefin material comprising one or more stabilizing compounds, wherein the stabilizing compounds are selected from the group consisting of non-chlorine-containing benzotriazole compounds, non-chlorine-containing triazine compounds, and non-chlorine-containing hydroxybenzophenone compounds. 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 mitigate 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 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 a variety of polymers with different chemical compositions; at the user level, such as in households, the knowledge and means to allow a user to separate one type of polymer from others are generally not available and not to be expected. And although certain plastic sorting technologies are available and are increasingly developed, the current situation is still that in practice the vast majority of waste plastic streams contain polymeric materials with disparate 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 particular route for processing mixed streams of waste polymers that has gained acceptance is via a chemical recycling route. Such routes typically 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 that 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 chlorine. The presence of chlorine can cause corrosion of equipment employed in unit operations for producing chemical compositions containing ethylene and propylene, such as in steam cracking operations.

[0008] To mitigate this issue, methods in the art provide separation unit operations for capturing chlorine-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 comes at a cost, involves additional energy consumption, and results in a reduced process yield. Accordingly, there is a desire to employ methods that must incorporate the fewest number of 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 a 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 the composition of polymers contains at most 10 ppm by weight of chlorine atoms relative to the total weight of the composition of polymers;

[0015] wherein the composition of polymers contains a polyolefin material containing one or more stabilizing compounds, wherein the stabilizing compounds are selected from non-chlorine-containing benzotriazole compounds, non-chlorine-containing triazine compounds, and non-chlorine-containing hydroxybenzophenone compounds.

[0016] 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 operations where chemical recycling includes steam cracking, this method allows for 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.

[0017] The preferred stabilizing compounds are selected from 2-(2'-hydroxy-3',5'-di-tert-butylphenyl)-benzotriazole, 2-(2'-hydroxy-3',5'-tert-amylphenyl)benzotriazole, 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-(2'-hydroxy-5'-tert-butylphenyl)benzotriazole, 2-(2'-hydroxy-5'-tert-octylphenyl)benzotriazole, 1,6-hexanediol bis(benzotriazol-2-yl-5-tert-butyl-4-hydroxyhydrocinnamate), 2,4-bis(2,4-dimethylphenyl)-6-(2-hydroxy-4-octyloxyphenyl)-1,3,5-triazine, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-n-octyloxybenzophenone, 2-hydroxy-4-n-dodecyloxybenzophenone, 2,4-dihydroxybenzophenone, 2-hydroxy-4-acryloxybenzophenone, 2-hydroxy-4-(benzyloxy)benzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, 2,2',4,4'-tetrahydroxybenzophenone, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, 2-hydroxy-4-allyloxybenzophenone, 2-hydroxy-4-(2-hydroxyethoxy)benzophenone, and 1,4-bis(4-benzoyl-3-hydroxyphenoxy)butane.

[0018] For example, the composition of the polymer may comprise a stabilizing compound in an amount of ≤5000 ppm by weight, preferably ≥500 and ≤5000 ppm, more preferably ≥500 and ≤3000 ppm, based on the total weight of the composition of the polymer.

[0019] Preferably, the composition of the polymer comprises chlorine atoms in an amount of ≥1 ppb by weight, preferably ≥5 ppb, more preferably ≥10 ppb, based on the total weight of the composition of the polymer.

[0020] Preferably, the composition of the polymer comprises ≤5 ppm by weight of chlorine atoms.

[0021] The heat treatment in step ii may include, for example, a mild pyrolysis process in which 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 in which the pyrolysis of the composition of the polymer is carried out at a temperature of >450 °C and ≤650 °C.

[0022] Alternatively, the heat treatment may be a catalytic process, preferably a process operated in the presence of a ZSM-5 zeolite catalyst and / or a spent FCC catalyst.

[0023] In the process 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.

[0024] For example, the hydrotreating step iii. can be carried out in the presence of a catalyst selected from: cobalt-molybdenum catalysts on alumina supports, nickel-molybdenum catalysts on alumina supports, tungsten-molybdenum catalysts on alumina supports, platinum-palladium catalysts on alumina supports, nickel sulfide catalysts, molybdenum sulfide catalysts, or nickel-molybdenum sulfide catalysts.

[0025] The thermal decomposition process of step iv. can be a steam cracking process, preferably where the steam cracking occurs in a steam cracking unit comprising heating coils, where the coil outlet temperature (COT) is from 800 °C to 870 °C. Alternatively, the thermal decomposition process of step iv. can be a catalytic cracking process.

[0026] In embodiments where the thermal decomposition process of step iv. is a steam cracking process, the feed composition supplied to the steam cracking process can for example comprise ≥ 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.

[0027] Alternatively, the feed composition supplied to the steam cracking process can for example comprise ≥ 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.

[0028] In the process of the present invention, the composition of the polymer can for example comprise, based on the total weight of the composition of the polymer:

[0029] · ≥ 70.0 wt% of a polyolefin composition;

[0030] · ≤ 20.0 wt% of a polyester composition;

[0031] · ≤ 20 wt% of a polyamide composition; and

[0032] · ≤ 10 ppm by weight, preferably ≥ 1 ppb and ≤ 10 ppm, more preferably ≥ 10 ppb and ≤ 5 ppm of chlorine atoms.

[0033] The present invention also relates to a composition of a polymer, which comprises, based on the total weight of the composition of the polymer:

[0034] · ≥ 70.0 wt% of a polyolefin composition;

[0035] · ≥ 0.1 and ≤ 20.0 wt% of a polyester composition;

[0036] · ≥ 0.1 and ≤ 20 wt% of a polyamide composition; and

[0037] · Chlorine atoms in an amount of ≤ 10 ppm by weight, preferably ≥ 1 ppb and ≤ 10 ppm, more preferably ≥ 10 ppb and ≤ 5 ppm.

[0038] The composition of the polymer may for example comprise one or more stabilizing compounds, wherein the stabilizing compounds are selected from non-chlorinated benzotriazole compounds, non-chlorinated triazine compounds and non-chlorinated hydroxybenzophenone compounds.

[0039] The stabilizing compounds may for example be selected from 2-(2'-hydroxy-3',5'-di-tert-butylphenyl)-benzotriazole, 2-(2'-hydroxy-3',5'-tert-amylphenyl)benzotriazole, 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-(2'-hydroxy-5'-tert-butylphenyl)benzotriazole, 2-(2'-hydroxy-5'-tert-octylphenyl)benzotriazole, 1,6-hexanediol bis(benzotriazol-2-yl-5-tert-butyl-4-hydroxybenzoate), 2,4-bis(2,4-dimethylphenyl)-6-(2-hydroxy-4-octyloxyphenyl)-1,3,5-triazine, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-n-octyloxybenzophenone, 2-hydroxy-4-n-dodecyloxybenzophenone, 2,4-dihydroxybenzophenone, 2-hydroxy-4-acryloxybenzophenone, 2-hydroxy-4-(benzyloxy)benzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, 2,2',4,4'-tetrahydroxybenzophenone, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, 2-hydroxy-4-allyloxybenzophenone, 2-hydroxy-4-(2-hydroxyethoxy)benzophenone, and 1,4-bis(4-benzoyl-3-hydroxy phenoxy)butane.

[0040] Particularly preferably, the composition of the polymer is obtained as a waste plastic stream, for example a waste plastic stream from post-consumer or household waste.

[0041] The invention also relates to the use of the composition of the polymer according to the invention for reducing fouling and / or corrosion in the steam cracking process of a chemical feedstock comprising waste plastic sources.

[0042] This method can effectively chemically recycle the polymer using a simplified process, in which the corrosion of the equipment used in the method is reduced.

[0043] The amount of chlorine atoms in the composition of the polymer may for example be determined according to ASTM UOP 779-08.

[0044] The hydrotreating process of step iii. can be carried out, for example, in one or more vessels configured to accommodate a hydrotreating catalyst. The vessels can be configured to operate in the gas phase, liquid phase, vapor-liquid phase, or slurry phase. The vessels 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 vessels can operate under adiabatic, isothermal, non-adiabatic, or non-isothermal conditions.

[0045] In the hydrotreating step, the product of step ii. can be treated in the presence of hydrogen, where the volume flow rate ratio of hydrogen to the product of step ii. can be, for example, 10 to 3000, preferably 200 to 1000.

[0046] 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 the following: 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.

[0047] The catalyst that can be used in the hydrotreating step iii. can be, for example, sulfided.

[0048] The composition of the polymer preferably contains ≥70.0 wt% of polyolefins. Such polyolefins preferably contain polyethylene and polypropylene. Specifically, the polyolefins can contain ≥80.0 wt% of polyethylene or ≥90.0 wt% of polyethylene. The polyolefins can contain ≤20.0 wt% of polypropylene or ≤10.0 wt% of polypropylene.

[0049] Such polyethylene can be a composition containing low-density polyethylene, linear low-density polyethylene, and high-density polyethylene.

[0050] Particularly preferably, the composition of the polymer contains a high proportion of polyolefins, such as ≥70.0 wt% or ≥80.0 wt% or ≥90.0 wt% based on 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 catalytic or non-catalytic heat treatment processes.

[0051] 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.

[0052] 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 of material use.

Claims

1. A method for the chemical recycling of a polymer, the method comprising the following steps: 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 the composition of the polymer comprises at most 10 ppm by weight of chlorine atoms relative to the total weight of the composition of the polymer; wherein the composition of the polymer comprises a polyolefin material containing one or more stabilizing compounds, wherein the stabilizing compounds are selected from non-chlorinated benzotriazole compounds, non-chlorinated triazine compounds, and non-chlorinated hydroxybenzophenone compounds.

2. The method according to claim 1, wherein the stabilizing compounds are selected from 2-(2'-hydroxy-3',5'-di-tert-butylphenyl)-benzotriazole, 2-(2'-hydroxy-3',5'-tert-amylphenyl)benzotriazole, 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-(2'-hydroxy-5'-tert-butylphenyl)benzotriazole, 2-(2'-hydroxy-5'-tert-octylphenyl)benzotriazole, 1,6-hexanediol bis(benzotriazol-2-yl-5-tert-butyl-4-hydroxybenzoate), 2,4-bis(2,4-dimethylphenyl)-6-(2-hydroxy-4-octyloxyphenyl)-1,3,5-triazine, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-n-octyloxybenzophenone, 2-hydroxy-4-n-dodecyloxybenzophenone, 2,4-dihydroxybenzophenone, 2-hydroxy-4-acryloyloxybenzophenone, 2-hydroxy-4-(benzyloxy)benzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, 2,2',4,4'-tetrahydroxybenzophenone, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, 2-hydroxy-4-allyloxybenzophenone, 2-hydroxy-4-(2-hydroxyethoxy)benzophenone, and 1,4-bis(4-benzoyl-3-hydroxyphenoxy)butane.

3. The method according to any one of claims 1-2, wherein the composition of the polymer comprises ≥1 ppb by weight of chlorine atoms relative to the total weight of the composition of the polymer.

4. The method according to any one of claims 1-3, 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.

5. The method according to any one of claims 1-4, 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.

6. The method according to any one of claims 1 - 5, 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.

7. The method according to any one of claims 1 - 6, wherein the hydrotreating step iii. is carried out in the presence of a catalyst, and the catalyst is selected from: cobalt - molybdenum catalyst on an alumina support, nickel - molybdenum catalyst on an alumina support, tungsten - molybdenum catalyst on an alumina support, platinum - palladium catalyst on an alumina support, nickel sulfide catalyst, molybdenum sulfide catalyst, or nickel - molybdenum sulfide catalyst.

8. The method according to any one of claims 1 - 7, 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, and 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.

9. The method according to claim 8, 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.

10. The method according to any one of claims 1 - 9, wherein the polymer composition comprises, based on the total weight of the polymer composition: · ≥70.0 wt% of a polyolefin composition; · ≤20.0 wt% of a polyester composition; · ≤20 wt% of a polyamide composition; and ≤10 ppm by weight, preferably ≥1 ppb by weight and ≤10 ppm by weight, more preferably ≥10 ppb by weight and ≤5 ppm by weight of chlorine atoms.

11. A polymer composition, which comprises, based on the total weight of the polymer composition: · ≥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 · ≤10 ppm by weight, preferably ≥1 ppb by weight and ≤10 ppm by weight, more preferably ≥10 ppb by weight and ≤5 ppm by weight of chlorine atoms.

12. The composition according to claim 11, wherein the polymer composition comprises one or more stabilizing compounds, and the stabilizing compounds are selected from non - chlorine - containing benzotriazole compounds, non - chlorine - containing triazine compounds, and non - chlorine - containing hydroxybenzophenone compounds.

13. The composition according to claim 12, wherein the stabilizing compound is selected from 2-(2'-hydroxy-3',5'-di-tert-butylphenyl)-benzotriazole, 2-(2'-hydroxy-3',5'-tert-amylphenyl)benzotriazole, 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-(2'-hydroxy-5'-tert-butylphenyl)benzotriazole, 2-(2'-hydroxy-5'-tert-octylphenyl)benzotriazole, 1,6-hexanediol bis(benzotriazol-2-yl-5-tert-butyl-4-hydroxybenzoate), 2,4-bis(2,4-dimethylphenyl)-6-(2-hydroxy-4-octyloxyphenyl)-1,3,5-triazine, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-n-octyloxybenzophenone, 2-hydroxy-4-n-dodecyloxybenzophenone, 2,4-dihydroxybenzophenone, 2-hydroxy-4-acryloxybenzophenone, 2-hydroxy-4-(benzyloxy)benzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, 2,2',4,4'-tetrahydroxybenzophenone, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, 2-hydroxy-4-allyloxybenzophenone, 2-hydroxy-4-(2-hydroxyethoxy)benzophenone, and 1,4-bis(4-benzoyl-3-hydroxyphenoxy)butane.

14. The method according to any one of claims 11-13, wherein the composition is obtained as a waste plastic stream from post-consumer waste.

15. Use of the polymer composition according to any one of claims 11-14 for reducing fouling and / or corrosion in the steam cracking process of a chemical feed of a material comprising a waste plastic source.