WO2023094629A1

WO2023094629A1 - A method for the removal of impurities from a pyrolysis oil

Info

Publication number: WO2023094629A1
Application number: PCT/EP2022/083355
Authority: WO
Inventors: Pierre Moreau; George Hargreaves
Original assignee: Plastic Energy Limited
Priority date: 2021-11-25
Filing date: 2022-11-25
Publication date: 2023-06-01
Also published as: GB2613166A; GB202116988D0

Abstract

There is provided a method for the removal of impurities from a pyrolysis oil obtained from the pyrolysis of end-of-life plastics, the method comprising: contacting the pyrolysis oil with an absorbent selected from the group consisting of a large pore zeolite, activated alumina and a mixture thereof, to obtain a purified pyrolysis oil.

Description

A method for the removal of impurities from a pyrolysis oil

The present invention relates to a method for the removal of impurities from a pyrolysis oil and, in particular, a readily performed single-pass treatment suitable to render the oil appropriate for use as a feedstock for cracking processes or for use as a transport fuel.

End-of-life plastic chemical recycling is an emerging technology designed to recycle mixed waste-plastics into a variety of liquid hydrocarbon products. The waste plastics for use in such a process may, for example, include low density polyethylene (LDPE), high density polyethylene (HDPE), polystyrene (PS), and/or polypropylene (PP).

Pyrolysis treatments are known for converting these waste plastics into the liquid hydrocarbon products by heating and then pumping the plastic feed in molten form into reactor vessels. The reactor vessels are heated by combustion systems to a temperature in excess of 350°C. This produces rich saturated hydrocarbon vapour from the molten plastic. This flows out of the reactor vessels through contactor vessels and will condense the heavier vapour fractions to maintain a target outlet temperature set point which is determined by the end-product specification. This is then distilled at near-atmospheric pressures in a downstream condensing column. This process obtains a so-called pyrolysis oil.

WO2021123822 discloses a method for pyrolysing plastic material. The method comprises the steps of: heating and densifying plastic material; transporting the plastic material to one or more reactors; and pyrolysing the plastic material in the one or more reactors. The plastic material is maintained in a heated state during the transporting step.

WO2016030460 discloses a pyrolysis reactor system suitable for the treatment of end-of-life plastics.

WO2011077419 also discloses a process for treating waste plastics material to provide at least one on-specification fuel product. Plastics material is melted (4) and then pyrolysed in an oxygen-free atmosphere to provide pyrolysis gases. The pyrolysis gases are brought into contact with plates (13) in a contactor vessel (7) so that some long chain gas components condense and return to be further pyrolysed to achieve thermal degradation. Short chain gas components exit the contactor in gaseous form; and proceed to distillation to provide one or more on-specification fuel products. There is a pipe (12) directly linking the pyrolysis chamber (6) to the contactor (7), suitable for conveying upwardly-moving pyrolysis gases and downwardly-flowing long-chain liquid for thermal degradation. There is a vacuum distillation tower (26) for further processing of liquid feeds from the first (atmospheric) distillation column (20). It has been found that having thermal degradation in the contactor and pyrolysis chamber and by having a second, vacuum, distillation column helps to provide a particularly good quality on-specification liquid fuel.

All of these foregoing methods and processes are suitable for obtaining a pyrolysis oil which can be used as a fuel, especially for transportation purposes, or for use as a cracking feedstock for producing monomers for fresh plastic manufacture.

US5107061 is directed to the removal of organochlorides from hydrocarbon streams using highly crystalline molecular sieve material, such as zeolites, and particularly zeolite X in a sodium form, and the removal of organochlorides from hydrocarbon streams containing olefinic compounds using such molecular sieves in combination with alumina for the purpose of effecting a decomposition of the organochloride into a corresponding unsaturated hydrocarbon molecule and a molecule of hydrocarbon chloride, wherein the hydrocarbon chloride is removed from the hydrocarbon stream by being adsorbed onto the adsorbent of the highly crystalline molecular sieve so that the unsaturated hydrocarbon molecule may be recovered from the resultant hydrocarbon stream containing a reduced amount of organochlorides.

US4721824 relates to a method for removing trace amounts of organic chlorides from feedstocks by passing the feedstock in contact with a guard bed catalyst comprising shaped particles formed by extruding a mixture of magnesium oxide and a binder inert to the feedstock. The process has particular importance in removing organic chlorides from toluene feedstocks prior to contacting toluene with a disproportionation or alkylation catalyst comprising magnesium-ZSM-5.

US3862900 relates to a method for treating hydrocarbons containing chemically combined chlorine by passing the hydrocarbons through a bed of molecular sieves of effective pore size in the range of 7 to 11 Angstrom units to remove the chemically combined chlorine and other impurities.

EP1728551 relates to desulfurization of gasoline cut by adsorption on a faujasite zeolite. This has a silicon/aluminium molar ratio of 1 -10, a meso and macroporosity volume of 0.25-0.4 cm³/g, a microporosity volume of 0.12-0.35 cm³/g and a size of crystals less than 3 microns. GB2163177 relates to a hydrocarbon conversion process wherein a hydrocarbon feed is contacted with a highly selective dehydrocyclization catalyst in a reaction zone to produce a product stream having a high aromatic hydrocarbon contact and then the paraffins in the product stream are extracted and recycled to the reaction zone.

EP0361681 relates to a process for purifying linear paraffins by removing therefrom contaminants such as aromatic compounds, sulfur- and nitrogen-containing compounds, and oxygen-containing compounds such as phenolics.

W02008013519 relates to a process for removing oxygenates Cw to C15 paraffins or a mixture of paraffins and olefins prior to use of these paraffins or olefins or mixtures thereof in further processes or reactions.

WO2012170034 relates to systems and methods for removing elemental sulfur from a hydrocarbon fluid using an adsorbent.

EP3907267 relates to a process for purifying a crude pyrolysis oil originating from the pyrolysis of plastic waste to obtain a purified pyrolysis oil having a reduced nitrogen, sulfur and halogen content in relation to the provided crude pyrolysis oil.

WO2021080899 relates to methods and systems for removing silicon and/or mercury contaminants from plastic-derived pyrolysis oil.

US2018230361 is directed toward the loading of liquids, solids dissolved in liquids (known as solutions), suspensions, and solids heated to reduce viscosity, onto scoria, perlite, pumice, aerogels, activated alumina, fullerenes, graphite, molybdenum, magnetite, vermiculite, and activated charcoal to achieve a dry liquid concentrate ("DLC") or slurry, for use in processes where a substance or substrate is to be expanded by a pressurized propellant and held in an expanded state by a proppant of granular solid material.

Accordingly, it is an object of the present invention to provide a method of providing an improved pyrolysis oil with advantageously reduced impurity levels, or at least to tackle problems associated therewith in the prior art, or provide a commercially viable alternative thereto.

According to a first aspect there is provided a method for the removal of impurities from a pyrolysis oil obtained from the pyrolysis of end-of-life plastics, the method comprising: contacting the pyrolysis oil with an absorbent selected from the group consisting of a large pore zeolite, activated alumina and a mixture thereof, to obtain a purified pyrolysis oil.

The present disclosure will now be described further. In the following passages different aspects/embodiments of the disclosure are defined in more detail. Each aspect/embodiment so defined may be combined with any other aspect/embodiment or aspects/embodiments unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous. It is intended that the features disclosed in relation to the product may be combined with those disclosed in relation to the method and vice versa.

The present inventors have found that there are particular issues with the use of pyrolysis oils obtained from pyrolysis of end-of-life plastics when seeking to use the pyrolysis oil as a feedstock for a cracking process, or even when using the oil as a transportation fuel. In particular, compared to natural oil materials, the pyrolysis oil obtained from end-of-life plastics has unacceptably high levels of mercury and phosphorous, as well as the typical sulphur and chlorine contaminants. Without wishing to be bound by theory, it is considered that the level of these impurities is a direct result of contaminants mixed with the plastics from their original lifetime use.

The levels of contaminants can require the downstream treatment processes to be halted if they build up to sufficient levels to poison the active catalysts used therein. In particular, phosphorus and mercury poisoning of zeolitic cracking catalysts can require production to be undesirably halted.

The inventors have therefore sought an optimised method for addressing the unique balance of impurities present in a pyrolysis oil obtained from end-of-life plastics. After testing a range of different materials, they have found that a small group of specific absorbents are capable of reducing the impurity levels sufficiently to mitigate the effect on downstream processes, especially in single-pass purification processes which are desirable when treating high volumes of material. Advantageously, these absorbents are able to treat both phosphorus and mercury to a sufficient level, while also having a beneficial effect on sulphur and chlorine impurities which may be present.

While it is known that similar zeolites can be used for sulphur and chlorine reduction in conventional oil feedstocks, as shown in the acknowledged prior art above, the sulphur treatment properties of the selected absorbents is not especially good. Indeed, only a 20% reduction is achieved on the more desirable continuous processing. Accordingly, the selection of such zeolites for treating a pyrolysis oil containing high levels of phosphorus and mercury impurities would not be an obvious selection.

The present invention provides a method for the removal of impurities from a pyrolysis oil obtained from the pyrolysis of end-of-life plastics. End-of-life or contaminated plastic waste feedstock, for plastic chemical recycling, may be received from, for example, municipal recovery facilities, recycling factories, or other plastic collection sources. During a pretreatment process, the feedstock may be refined such that it only contains plastics suitable for the chemical recycling process, preferably hydrocarbon plastics. Such plastics are those that are formed of hydrocarbons (and therefore consist essential of carbon and hydrogen). Preferably, the hydrocarbon plastic is polyethylene (PE), such as low density polyethylene (LDPE) and/or high density polyethylene (HDPE), polystyrene (PS), and/or polypropylene (PP). Unsuitable materials, such as metals, paper and card, and glass, as well as humidity from the plastic waste, may be removed.

As will be appreciated, the recycling of end-of-life plastics introduces various impurities that are preferably removed from the feedstock before recycling during the pre-treatment, for example by washing. Preferably, the ELP feedstock comprises at least 80 wt% plastic, more preferably at least 90 wt% plastic and most preferably consists essentially of plastic.

A pyrolysis oil is obtained by the thermal treatment of these plastics materials.

WO2021 123822 discloses an optimised process for this pyrolysis and the contents of this document are incorporated herein in their entirety by reference. This sort of pyrolysis oil, because of its source, contains a number of impurities, including: Sulphur; Chlorine; Phosphorus; Metals: especially mercury, but also arsenic, lead, nickel and the like; Silica; Oxygen and Nitrogen. As will be appreciated, the elements, in particular the metals, may be present in their elemental form though will typically be present as compounds such as salts and/or organic impurities comprising said elements (i.e. organosulphur impurities and so forth).

The present method comprises contacting the pyrolysis oil with an absorbent selected from the group consisting of a large pore zeolite, activated alumina and a mixture thereof, to obtain a purified pyrolysis oil.

Zeolites are well known for use in various industrial treatment processes and are commonly categorised by their pore sizes. In particular, there is a focus on the number of atoms which form their largest ring size, since this is a practical limitation on the ease with which molecules can diffuse into and out of the zeolite during a process. A small pore zeolite has a ring of 8 atoms, whereas a medium pore zeolite has a ring of 10 atoms and a large pore zeolite has a ring of 12 atoms. The zeolite used is preferably an aluminosilicate zeolite, having a framework consisting of Al and Si atoms. A further characteristic of zeolites is the form in which they are supplied, such as the Na+ or H+ form. In addition, the zeolites can be substituted with additional metal species, especially for catalytic purposes, such as the introduction of copper for SCR catalysts.

The optimised zeolite for use in the present method is a large pore zeolite and, in particular, preferably the absorbent comprises a zeolite having the FAU framework-type. Examples of this zeolite include 13X from BASF. Preferably the zeolite is used in the Na-exchanged form. Preferably the zeolite is free from any added metals. That is, preferably the zeolite consists of AI2O3 and SiO2 (i.e. an aluminosilicate), and when in the Na-exchanged form Na2© (i.e. a sodium aluminosilicate).

The absorbent may also or instead comprise activated alumina. An activated alumina is well known in the art and refers to dehydroxylated alumina hydroxide which has a particularly high surface area. Preferably the activated alumina has a surface area as measured by Nitrogen BET of at least 25 m²/g, more preferably at least 100 m²/g and most preferably 125 m²/g to 250 m²/g.

The present inventors have further found that the use of an absorbent comprising both a large-pore zeolite and the activated alumina is particularly effective for treating pyrolysis oil. This is because the various strengths and weaknesses of the two different types of material are complementary. Preferably the absorbent comprises a mixture of a large pore zeolite and activated alumina in a weight ratio of from 2:1 to 1 :2, more preferably about 1 :1 .

The purified pyrolysis oil contains a reduced amount of impurity species. In a particularly preferred embodiment of the present invention, the pyrolysis oil contains mercury, phosphorus, sulphur and chlorine impurities and the method comprises contacting such pyrolysis oil with an absorbent consisting of a large pore zeolite, and optionally activated alumina, to obtain a purified pyrolysis oil having a reduced amount of each said impurities. More particularly, it is preferred that the reduced amount of each of the impurities (Hg, P, S and Cl) are present in an amount of 80% or less by weight of the initial amount of the respective impurity. That is, there is a 20% reduction or more in the amount of each of Hg, P, S and Cl. More preferably, the reduced amount is 70% or less. Preferably, the reduced amount of mercury is 50% or less, more preferably 25% or less. Preferably, the reduced amount of phosphorus is 60% or less, more preferably 50% or less. Preferably, the reduced amount of sulphur is 60% or less, more preferably 40% or less. Preferably, the reduced amount of chlorine is 60% or less, more preferably 50% or less.

For example, typically a pyrolysis oil comprises at least (by weight on an elemental basis): 140 ppm Sulphur, more preferably at least 200 ppm Sulphur;

100 ppm Phosphorus, more preferably at least 150 ppm Phosphorus; 500 ppb Mercury, more preferably at least 750 ppb Mercury;

600 ppm Chlorine, more preferably at least 800 ppm Chlorine.

Advantageously, the process of the invention can provide a purified pyrolysis oil which comprises at most:

110 ppm Sulphur, more preferably at most 80 ppm; 50 ppm Phosphorus, more preferably at most 30 ppm; 200 ppb Mercury, more preferably at most 150 ppb; 300 ppm Chlorine, more preferably at most 200 ppm.

The method described herein can be performed on a batch or continuous basis. Continuous treatment is preferred when there is a continuous large supply of pyrolysis oil available for treatment. Batch processes are more desirable where there are smaller volumes of oil being produced, or where it is being produced on an intermittent basis. In a batch process there may be a plurality of holding vessels used in parallel, giving a quasi-continuous effect on the treatment performed.

According to one embodiment, the step of contacting the pyrolysis oil with an absorbent is performed in a batch method. In this method the pyrolysis oil to be treated is loaded into a holding vessel for a specific treatment time where it contacts the absorbents. The holding vessel may be fitted with means for providing agitation. Preferably the pyrolysis oil is contacted with the absorbent for a treatment time of at least 10 minutes, preferably from 15 minutes to 1 hour. Preferably, the pyrolysis oil is contacted with the absorbent in an amount of from 1 to 20 mL of oil per gram of absorbent, more preferably from 2 to 10 mL of oil per gram of absorbent. The present invention is particularly suited to removing impurities from a relatively large quantity of oil with a relatively small quantity of absorbent. More particularly, the present invention allows for the removal of multiple impurities simultaneously in an efficient manner with only a relatively small quantity of the absorbent. The process is particularly efficient where the absorbent is then used to contact the oil in only a single pass to remove such impurities.

According to another embodiment, the step of contacting the pyrolysis oil with an absorbent is performed in a continuous method. In this method the pyrolysis oil is passed through a treatment bed filled with the absorbent. Preferably the pyrolysis oil is contacted with the absorbent in a single pass treatment through a single bed of the absorbent. This allows for fast efficient treatments without requiring high storage volumes. With a continuous process the production and use of the pyrolysis oil can be integrated into a continuous process. Preferably the pyrolysis oil is contacted with the absorbent in a continuous process at a rate of at most 1 mL of oil per gram of absorbent per minute, more preferably at most 0.5 mL of oil per gram of absorbent per minute. Preferably, the pyrolysis oil is contacted with the absorbent in a continuous process at a rate of at least 0.1 mL of oil per gram of absorbent per minute more preferably at least 0.2 mL of oil per gram of absorbent, for example from 0.1 mL to 1 mL of oil per gram of absorbent.

Preferably the absorbent is intermittently regenerated by a thermal treatment. That is, when the absorbent has become loaded or saturated with impurities to the point where its performance is reduced, the absorbent can be thermally treated, preferably in air, to remove the contaminants as an exhaust gas which can be captured and processed in conventional ways to neutralise or capture the impurity material.

According to a further aspect, there is provided a method for treating end-of-life plastics, the method comprising: pyrolysing end-of-life plastics to obtain a pyrolysis oil; performing the method disclosed herein to provide a purified pyrolysis oil; and cracking the purified pyrolysis oil to provide monomer species for the manufacture of a polymeric plastic material.

Methods for cracking pyrolysis oil to obtain a useful feedstock of monomers for further plastic production are also known in, for example, US5731483, which is incorporated herein by reference.

Methods for pyrolysis end-of-life plastics are well known in the art, including, for example, in WO2021123822, WO2016030460 and WO2011077419 which are each incorporated herein by reference. The preferred method of pyrolysis will now be described further in more detail. Preferably the method for pyrolysis end-of-life plastics involves the steps of: melting a waste plastics material, pyrolysing the molten material in an oxygen-free atmosphere to provide pyrolysis gases; bringing the pyrolysis gases into a contactor having a bank of condenser elements so that some long chain gas components condense on said elements, returning said condensed long-chain material to be further pyrolysed to achieve thermal degradation, and allowing short chain gas components to exit from the contactor in gaseous form; and distilling said pyrolysis gases from the contactor in a distillation column to provide one or more fuel products.

Preferably the contactor elements comprises a plurality of plates forming an arduous path for the pyrolysis gases in the contactor. Moreover, preferably the plates are sloped downwardly for runoff of the condensed long-chain hydrocarbon, and include apertures to allow upward progression of pyrolysis gases. In one embodiment, the contactor elements comprise arrays of plates on both sides of a gas path. Preferably the contactor element plates are of stainless steel. The contactor may be actively cooled such as by a heat exchanger for at least one contactor element.

Alternative cooling means may comprise a contactor jacket and cooling fluid is directed into the jacket. There may be a valve linking the jacket with a flue, whereby opening of the valve causing cooling by down-draught and closing of the valve causing heating. The valve may provide access to a flue for exhaust gases of a combustion unit of the pyrolysis chamber.

Preferably there is a pipe directly linking the pyrolysis chamber to the contactor, the pipe being arranged for conveying upwardly-moving pyrolysis gases and downwardly-flowing long-chain liquid for thermal degradation.

Preferably infeed to the pyrolysis chamber is controlled according to monitoring of level of molten plastics in the chamber, as detected by a gamma radiation detector arranged to emit gamma radiation through the chamber and detect the radiation on an opposed side, intensity of received radiation indicating the density of contents of the chamber.

Preferably the pyrolysis chamber is agitated by rotation of at least two helical blades arranged to rotate close to an internal surface of the pyrolysis chamber. Optionally, the pyrolysis chamber is further agitated by a central auger. Advantageously, the auger can be located so that reverse operation of it causes output of char via a char outlet.

Preferably the temperature of pyrolysis gases at an outlet of the contactor is maintained in the range of 240°C to 280°C. The contactor outlet temperature can be maintained by a heat exchanger at a contactor outlet.

A bottom section of the distillation column is preferably maintained at a temperature in the range of 200°C to 240°C, preferably 210°C to 230°C. The top of the distillation column is preferably maintained at a temperature in the range of 90°C to 110°C, preferably approximately 100°C.

Optionally there is further distillation of some material in a vacuum distillation column. Heavy or waxy oil fractions are drawn from the bottom of the vacuum distillation column and can be recycled back to the pyrolysis chamber. Desired grade on-specification pyrolysis oil can be drawn from a middle section of the vacuum distillation column. Light fractions are drawn from a top section of the vacuum distillation column and are condensed.

According to a further aspect, there is provided a method for the manufacture of a polymeric plastic material, the method comprising: performing the method described herein for treating end-of-life plastics, and polymerising the monomer species, optionally together with further monomer species, to form a polymeric plastic material.

Polymerisation techniques for making fresh plastics from the polymerisation of monomers are well known in the art.

According to a further aspect there is provided the use of a large pore zeolite to reduce the amount of one or more of phosphorus, mercury, sulphur and chlorine impurities from a pyrolysis oil obtained from the pyrolysis of end-of-life plastics. Preferably this use includes reducing levels of all four of the listed impurities (i.e. simultaneously). More preferably, the large pore zeolite is used in an amount of at most 1 g of absorbent per mL of oil, preferably at most 0.5 g of absorbent per mL of oil. The preferred absorbents discussed in the aspects above, and the disclosed method features, apply equally to the use set out in this aspect. Figures

The invention will now be described further in relation to the following non-limiting figures, in which:

Figure 1 shows the level of impurities in the pyrolysis oil, after the adsorbent bed, in the continuous treatment example.

In Figure 1 the substantially flat lowest line is phosphorus, the mostly flat line above this is sulphur, the heavily fluctuating line is mercury and the generally highest line is chlorine. The concentrations of the sulphur, chlorine and phosphorus are plotted against the left hand y-axis ranging from 0 to 350 ppm whereas the concentration of mercury, which is substantially absent from the purified pyrolysis oil, are plotted against the right hand y-axis ranging from 0.00 to 0.35 ppm.

Examples

The invention will now be described further in relation to the following non-limiting examples.

1. Batch reactor

In a batch reactor, 5 g of Molecular Sieve 13X (Na-form, FAU zeolite) were added to 25 mL of Pyrolysis Oil for a contact time of 50 min. Results are shown in the table below Table 1).

Table 1: Level of impurities after purification.

A significant reduction for all 4 impurities (sulphur, chlorine, phosphorus, and mercury) is observed for NaX Molecular Sieve whereas Activated Alumina is observed to provide only a minor reduction in Sulphur but provides a slightly better reduction in Chlorine and Phosphorus.

2. Flow reactor

1 g of NaX zeolite was packed into an adsorbent tube. 1 mL/min. of pyrolysis oil was flown over the bed in flow. Pyrolysis oil fractions were collected post reactor, every 2 min. Those fractions have been analysed using an Energy Dispersive X-Ray Analysis (EDX) instrument for level of Sulphur, Chlorine, Phosphorus, Mercury, and Silica: this instrument has been calibrated for these elements beforehand. Results are presented in Figure 1 and table below as a function of time.

Table 2: Level of impurities post adsorbent bed.

A decrease in level of impurities is as follow:

1. Sulphur: -20%

2. Chlorine: -50%

3. Phosphorus: -43%

4. Mercury: -100%

This demonstrate that molecular sieve 13X is well suited to remove impurities from a pyrolysis oil feedstock.

The term “comprising” as used herein can be exchanged for the definitions “consisting essentially of” or “consisting of”. The term “comprising” is intended to mean that the named elements are essential, but other elements may be added and still form a construct within the scope of the claim. The term “consisting essentially of” limits the scope of a claim to the specified materials or steps and those that do not materially affect the basic and novel characteristic(s) of the claimed invention. The term “consisting of” closes the claim to the inclusion of materials other than those recited except for impurities ordinarily associated therewith.

The foregoing detailed description has been provided by way of explanation and illustration, and is not intended to limit the scope of the appended claims. Many variations in the presently preferred embodiments illustrated herein will be apparent to one of ordinary skill in the art, and remain within the scope of the appended claims and their equivalents.

For the avoidance of doubt, the entire contents of all documents acknowledged herein are incorporated herein by reference.

Claims

Claims:

1 . A method for the removal of impurities from a pyrolysis oil obtained from the pyrolysis of end-of-life plastics, the method comprising: contacting the pyrolysis oil with an absorbent selected from the group consisting of a large pore zeolite, activated alumina and a mixture thereof, to obtain a purified pyrolysis oil.

2. The method according to claim 1 , wherein the step of contacting the pyrolysis oil with an absorbent is performed in a batch method.

3. The method according to claim 1 or claim 2, wherein the pyrolysis oil is contacted with the absorbent in an amount of from 1 to 20 mL of oil per gram of absorbent, preferably from 2 to 10 mL of oil per gram of absorbent.

4. The method according to claim 2, wherein the pyrolysis oil is contacted with the absorbent for a treatment time of at least 10 minutes and/or at most 60 minutes.

5. The method according to claim 1 , wherein the step of contacting the pyrolysis oil with an absorbent is performed in a continuous method.

6. The method according to any preceding claim, wherein the pyrolysis oil is contacted with the absorbent in a continuous process at a rate of at most 1 mL of oil per gram of absorbent per minute, preferably from 0.1 to 1 mL of oil per gram of absorbent per minute.

7. The method according to claim 4 or claim 5, wherein the pyrolysis oil is contacted with the absorbent in a single pass treatment through a single bed of the absorbent.

8. The method according to any preceding claim, wherein the absorbent comprises a zeolite having the FAU framework-type.

9. The method according to any preceding claim, wherein the activated alumina has a surface area as measured by Nitrogen BET of at least 25 m²/g.

10. The method according to any preceding claim, wherein the absorbent comprises a mixture of a large pore zeolite and activated alumina in a weight ratio of from 2:1 to 1 :2.

11 . The method according to any preceding claim, wherein the impurities are mercury, phosphorus, sulphur and chlorine impurities, the method comprising contacting the pyrolysis oil containing the mercury, phosphorus, sulphur and chlorine impurities with an absorbent consisting of a large pore zeolite, and optionally activated alumina, to obtain a purified pyrolysis oil having a reduced amount of each said impurities.

12. The method according to claim 11 , wherein the reduced amount is 80% or less preferably 70% or less.

13. The method according to claim 12, wherein the reduced amount of mercury is 50% or less, the reduced amount of phosphorus is 70% or less, the reduced amount of sulphur is 40% or less, and the reduced amount of chlorine is 60% or less.

14. The method according to any one of claims 11 to 13, wherein the large pore zeolite is in Na-exchanged form and has the FAU framework-type.

15. The method according to any preceding claim, wherein the pyrolysis oil comprises at least:

140 ppm Sulphur;

100 ppm Phosphorus;

500 ppb Mercury;

600 ppm Chlorine.

16. The method according to any preceding claim, wherein the purified pyrolysis oil comprises at most:

110 ppm Sulphur;

50 ppm Phosphorus;

200 ppb Mercury;

300 ppm Chlorine.

17. The method according to any preceding claim, wherein the absorbent is intermittently regenerated by a thermal treatment.

18. A method for treating end-of-life plastics, the method comprising: pyrolysing end-of-life plastics to obtain a pyrolysis oil; performing the method of any of claims 1 to 17 to provide a purified pyrolysis oil; and cracking the purified pyrolysis oil to provide monomer species for the manufacture of a polymeric plastic material.

19. A method for the manufacture of a polymeric plastic material, the method comprising: performing the method according to claim 18, and polymerising the monomer species, optionally together with further monomer species, to form a polymeric plastic material.

20. Use of a large pore zeolite to reduce the amount of one or more of phosphorus, mercury, sulphur and chlorine impurities from a pyrolysis oil obtained from the pyrolysis of end-of-life plastics.

21 . The use according to claim 20 to reduce the amounts of all of phosphorus, mercury, sulphur and chlorine impurities from the pyrolysis oil simultaneously.

22. The use according to claim 21 , wherein the large pore zeolite is used in an amount of at most 1 g of absorbent per mL of oil, preferably at most 0.5 g of absorbent per mL of oil.

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