Methods and compositions for chemical recovery of polymers with reduced silicon 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 silicon 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 the efficiency of the equipment employed in the process is improved. 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, specifically for a chemical recycling method that includes pyrolyzing a polymer composition to obtain pyrolysis oil and then 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 associated with polymeric materials, such as thermoplastics, there is an increasingly stringent drive to find applications where polymeric materials that are no longer considered useful for their original purpose can be meaningfully utilized while minimizing the environmental burden, such as through landfill disposal 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 the household, the knowledge and means to allow the user to separate one type of polymer from the others are generally not available and are not to be expected. And although certain plastic sorting technologies 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 particular route for processing mixed streams of waste polymers that has gained acceptance is via chemical recycling routes. 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 naphtha-type compositions obtainable from refined fossil crude oil. This stage can then be followed by processing such oily compositions via thermochemical decomposition methods 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 a (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 silicon. The presence of silicon can lead to a reduction in the efficiency of equipment employed in unit operations for the production of 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 trapping silicon-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 reduction in the process yield. Accordingly, it is desirable to employ methods that must incorporate the minimum 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 a polymer;

[0011] ii. Subjecting the composition of the polymer 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 the composition of the polymer contains at most 10 ppm by weight of silicon atoms relative to the total weight of the composition of the polymer.

[0015] This method can effectively chemically recycle polymers using a simplified process, wherein the efficiency of the equipment employed in the method is improved. For example, in an operation 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.

[0016] Preferably, the composition of the polymer contains ≥1 ppb by weight, preferably ≥5 ppb, more preferably ≥10 ppb of silicon atoms relative to the total weight of the composition of the polymer.

[0017] Preferably, the composition of the polymer contains ≤5 ppm by weight of silicon atoms.

[0018] The heat treatment in step ii may include, for example, a mild pyrolysis process in which the pyrolysis of the polymer composition is carried out at a temperature of ≥250°C and ≤450°C; or a severe pyrolysis process in which the pyrolysis of the polymer composition is carried out at a temperature of >450°C and ≤650°C.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] The thermal decomposition process in step iv may be a steam cracking process, preferably in which the steam cracking occurs in a steam cracking unit comprising 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.

[0023] 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.

[0024] 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.

[0025] In the method of the present invention, the polymer composition may, for example, contain, based on the total weight of the polymer composition:

[0026] · ≥70.0 wt% of a polyolefin composition;

[0027] · ≤20.0 wt% of a polyester composition;

[0028] · A polyamide composition of ≤ 20% by weight; and

[0029] · Silicon atoms of ≤ 10 ppm by weight, preferably ≥ 1 ppb and ≤ 10 ppm, more preferably ≥ 10 ppb and ≤ 5 ppm.

[0030] The present invention also relates to a polymer composition comprising, based on the total weight of the polymer composition:

[0031] · A polyolefin composition of ≥ 70.0% by weight;

[0032] · A polyester composition of ≥ 0.1% and ≤ 20.0% by weight;

[0033] · A polyamide composition of ≥ 0.1% and ≤ 20% by weight; and

[0034] · Silicon atoms of ≤ 10 ppm by weight, preferably ≥ 1 ppb and ≤ 10 ppm, more preferably ≥ 10 ppb and ≤ 5 ppm.

[0035] The polymer composition is particularly preferably obtained as a waste plastic stream, such as a waste plastic stream from post-consumer or household waste.

[0036] The present invention also relates to the use of the polymer composition according to the present invention for improving the efficiency in the steam cracking process of a chemical feed of a material containing a waste plastic source.

[0037] This method can effectively chemically recycle polymers using a simplified process.

[0038] The hydrotreating process in 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.

[0039] In the hydrotreating step, the product of step ii. can be treated in the presence of hydrogen, where the volume flow ratio of hydrogen to the product of step ii. can be, for example, 10 to 3000, preferably 200 to 1000.

[0040] 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.

[0041] The catalyst that can be used in the hydrotreating step iii. can be, for example, sulfided.

[0042] The composition of the polymer preferably contains ≥70.0 wt% of polyolefin. Such polyolefins preferably contain polyethylene and polypropylene. Specifically, the polyolefin can contain ≥80.0 wt% of polyethylene or ≥90.0 wt% of polyethylene. The polyolefin can contain ≤20.0 wt% of polypropylene or ≤10.0 wt% of polypropylene.

[0043] Such polyethylene can be a composition containing low-density polyethylene, linear low-density polyethylene, and high-density polyethylene.

[0044] Particularly preferably, the composition of the polymer contains a high proportion of polyolefin, 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 polyolefin 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.

[0045] Via such thermal cracking, such as steam cracking or catalytic cracking, the composition of plastics, particularly the composition of waste plastics, can be converted into chemical structural units, specifically ethylene and propylene.

[0046] Therefore, the method of the present invention allows 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 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 silicon atoms relative to the total weight of the composition of the polymer.

2. The method according to claim 1, wherein the composition of the polymer comprises ≥ 1 ppb by weight of silicon 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 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.

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

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

6. The method according to any one of claims 1-5, wherein the hydrotreating step iii. is carried out in the presence of a catalyst, wherein the catalyst is 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.

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

8. The method according to claim 7, 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.

9. The method according to any one of claims 1 - 8, wherein the polymer composition comprises, based on the total weight of the polymer composition: · ≥ 70.0% by weight of a polyolefin composition; · ≤ 20.0% by weight of a polyester composition; · ≤ 20% by weight of a polyamide composition; and · ≤ 10 ppm by weight of silicon atoms, preferably ≥ 1 ppb and ≤ 10 ppm, more preferably ≥ 10 ppb and ≤ 5 ppm.

10. A polymer composition comprising, based on the total weight of the polymer composition: · ≥ 70.0% by weight of a polyolefin composition; · ≥ 0.1 and ≤ 20.0% by weight of a polyester composition; · ≥ 0.1 and ≤ 20% by weight of a polyamide composition; and · ≤ 10 ppm by weight of silicon atoms, preferably ≥ 1 ppb and ≤ 10 ppm, more preferably ≥ 10 ppb and ≤ 5 ppm.

11. The composition according to claim 10, wherein the composition is obtained as a waste plastic stream from post - consumer waste.

12. Use of the polymer composition according to any one of claims 10 - 11 for improving efficiency in a steam cracking process of a chemical feed of a material comprising a waste plastic source.