Description

The invention relates to a method for producing a crude styrene oil mixture, rich in styrene and styrene derivatives, by pyrolysis of a polymer waste stream. The method involving a step of rapid phase separation. The method produces a pyrolysis oil (PO) containing vinylaromatic monomers (M) from a polymer (P) comprising repeating units of said monomers (M). The method comprises steps of pyrolysis of the polymer (P), quenching of the pyrolysis reaction with an aqueous solution (A) or water, phase separation and collecting of the organic phase as the pyrolysis oil (PO), wherein the step of quenching and/or the phase separation involve an aqueous solution of phosphate ions (PO ₄ ³ -).

Background

Climate change, environmental pollution, population growth and resource dependency trigger the ecological and economic necessity of the transition from a linear to a circular economy. Since the 1990s, intensive efforts to develop improved processes for the recovery of raw materials from recycling of plastic waste were made. These efforts have not yet resulted in large-scale applications, in particular due to unresolved process engineering problems and economic reasons, such as the non-availability of suitable materials. However, the topic of plastic waste as well as a greater ecological awareness and a need for sustainable solutions have led to a growing interest in chemical recycling.

Not all thermoplastic polymers are equally suited for chemical recycling. The thermal decomposition of polyolefins or polyesters results in mixtures of waxes, light oil and gases. The degradation of polyethylene terephthalate (PET) results in organic acids, mainly benzoic acid and terephthalic acid, which are corrosive and may also cause clogging of the reactor (G. Grause et al., Feedstock recycling of waste polymeric material, in: Journal of Material Cycles and Waste Management, 13(4), 2011 , 265-282).

In the case of polystyrene and other styrene-containing polymers, it is possible to depolymerize the polymers into the basic components, especially styrenic monomers, which make polystyrene and other styrene monomer-containing polymers excellent choices for chemical recycling. However, the resulting product mixture of a de-polymer- ization process needs to be purified in order to use the components as raw material for new purposes, such as polymerization processes. WO 2018/224482 (INEOS Styrolution) describes a method of pyrolytically de-polymeriz- ing a styrene-containing polymer waste plastic. EP-A 2635043, KR-A 2020 0016935 and CN-A 110869428 deal with de-polymerization as well.

The process of WO 2018/224482 comprises the steps: i) decomposing the styrene-containing polymer waste plastic (K) in a suitable reactor by thermal and optionally shearing energy, wherein the waste plastic (K) is sent to a pyrolysis zone of the reactor and pyrolyzed there, and wherein the styrene component of the waste plastic (K) is at least partly decomposed into styrene monomers and oligomers; ii) capturing the gases formed in step i) and condensing low molecular weight products, comprising the styrene monomers formed; iii) separating the condensed low molecular weight constituents, comprising the styrene monomers formed, via fractional distillation; and iv) sending the styrene oligomers formed in step i) to a steam cracker.

WO 2020/178597 (Oxford Sustainable Fuels Limited) describes a process for upgrading the quality of pyrolysis oil derived from plastic, rubber or a combination thereof, comprising the treatment of a pyrolysis oil with an aqueous solution and optionally a hydrocarbon fluid, wherein the process is intended to remove undesired contaminants from the pyrolysis oil or to enrich the pyrolysis oil with desired components.

WO 2021/110751 (INEOS Styrolution) describes thermoplastic compounds containing recycling material with superior quality. The main aspect of the invention relates to a thermoplastic molding composition (T) comprising recycled polymer material (A), containing ABS.

US 11041123 (Agilyx, 2020) describes systems and methods for recycling waste plastics, including a system for recovering styrene monomer from waste polystyrene. The system includes an apparatus to receive a supply of waste polystyrene and to output a densified polystyrene containing melt; a pyrolysis reactor configured to pyrolyze the densified polystyrene containing melt and recycled oligomers, and to output a hydrocarbon gas stream and a solids residue stream; a quenching apparatus configured to condense out oligomers for routing upstream to the pyrolysis reactor, and to discharge an altered hydrocarbon gas stream for further processing; and a condenser configured to receive the altered hydrocarbon gas stream from the quenching apparatus and condense out styrene to form a styrene monomer oil product.

WO 2021/180893 (Indaver) relates to a two-step pyrolysis process for recovering at least styrene monomer and other low molecular weight liquid polystyrene pyrolysis products from a plastic material containing polystyrene. After a first cracking step, two gaseous phases are separated and the heavier fraction comprising styrene oligomers is then further cracked. This enables the recovery of a higher amount of the low molecular weight liquid polystyrene pyrolysis products, including styrene monomer and other low molecular weight liquid products, such as alphamethylstyrene, cumene, ethyl-benzene and toluene.

In such thermal de-polymerization processes, wherein a styrene-containing polymer waste stream is converted to a crude styrene gas stream (CSG) that is rich in styrene and styrene derivatives, a cost- and energy-efficient and simple way of terminating the pyrolysis reaction and condensing the CSG stream into a crude styrene oil or pyrolysis oil (CSO) includes quenching the reaction with water. In continuous de-polymerization processes, typically a continuous stream of CSG is withdrawn from the de-polymeriza- tion reactor, which can then be quenched and condensed with water in a separate device. In a typical process, but not limited to this, the CSG is quenched with finely dispersed water droplets (i.e. a spray). The process can run in one single stage or multiple consecutive stages condensing different portions of the CSG into different fractions of the CSO. In at least one of these stages water is used as quenching and condensing medium but also other media, like hydrocarbons, can be used as quenching and condensing media. The quenching with water allows a fast termination and fast cooling of the CSG stream and hence, the formation of by-products downstream of the reactor, when the CSG is still hot, is reduced.

In the collection vessel after this quenching and condensation step, a stable emulsion and dispersion of the condensed CSO in water can occur. This considerably impedes further processing due to slow or completely absent phase separation into a clear aqueous layer and a CSO layer, which would allow the CSO layer to be separated (i.e. decanted). Such emulsions and dispersions can exist and remain stable even for several days. Although phase separation does occur to a certain extent, even immediately after quenching, it is usually only possible to collect a portion of the organic phase directly after quenching, followed by further processing, whereas the rest of the CSO remains dispersed in the aqueous phase. Furthermore, the aqueous phase containing CSO often cannot be recycled and utilized for quenching, since certain components in the CSO may damage or block conduits or other mechanical components used for transferring the aqueous phase back to the quenching device.

Especially on an industrial scale, it is inconvenient and cost-ineffective to wait for the CSO to separate from the aqueous phase, since the processes need to be interrupted eventually, to collect the CSO separating from the aqueous phase. This particularly applies to continuous processes on an industrial scale. Therefore, in continuous industrial processes, a large amount of the aqueous phase containing substantial amounts of CSO may have to be discarded, which is undesirable in terms of process efficiency and sustainability. Alternatively, other means for terminating the de-polymerization reaction, like classical condensation of the CSG at the cold walls of e.g. a tube-and-shell condenser, have to be employed instead of quenching and condensing with water, which, however decreases the styrene yield in the CSO due to the slow cooling process and resultant increased amount of formed by-products. In addition, this process is less efficient and may increase the complexity and costs of the process e.g. due to the high velocity of the CSG exiting the pyrolysis reactor.

CN 114053759 A (Th-Unis Insight, 2020) refers to a process for dehydrating aqueous organic compounds, wherein dehydration of a water-containing organic mixture is performed by adding salt. In several phase separation steps of the process, a dehydrating agent selected from anhydrous salt, hydrated salt, nearly saturated salt solution, saturated salt solution and/or supersaturated salt solution is added to the aqueous organic matter. The mixture is left to form an upper organic solution and a lower aqueous salt solution. In one step, the water content of the organic matter can be reduced from 30-40 wt.% to less than 10 wt.%.

JP 2018-103159 A (Kobelco Eco Solutions, 2016) relates to a water treatment method and a waste oil treatment method, especially to a method capable of reducing the phosphate ion concentration in an organic phase.

WO 2010/033789 and US 8741258 (University of Massachusetts) describes the processing of bio-oil derived from fast pyrolysis of biomass, which is a complex mixture of various compounds including water and organic solvents and materials. One processing step is an aqueous extraction to separate water-soluble and water-insoluble fractions. Additives may be included in the aqueous phase to facilitate the separation of the water- soluble and insoluble phases, in particular, salts and/or buffering agents may be added to increase the ionic strength of the aqueous phase to facilitate phase separation, and to adjust the pH of the resulting aqueous phase.

A process sufficiently satisfying all needs described above in terms of industrial application, sustainability, economy and efficiency of quenching, condensing and processing aqueous CSO mixtures is still not available.

An objective of the present invention is to provide a cost-efficient, preferably continuous, process for producing a pyrolysis oil (PO) from a pyrolysis gas stream containing vinylar- omatic monomers (M) from a polymer (P) comprising repeating units of said monomers (M), wherein the recovery rate of pyrolysis oil (PO) available after termination of the de- polymerization reaction is increased in relation to other processes known in the art. Preferably, the polymer originates from styrene-containing polymer waste. Accordingly, the pyrolysis oil is preferably a crude styrene pyrolysis oil (CSO).

Surprisingly, it was found that the rate of phase separation between pyrolysis oil containing vinylaromatic monomers (M) and water, and

Therefore, a first aspect of the invention is a method for producing a pyrolysis oil (PO) containing vinylaromatic monomers (M), preferably styrene, from a polymer (P) comprising repeating units of said monomers (M), wherein the method comprises the steps: a. Pyrolysis of the polymer (P) comprising repeating units of vinylaromatic monomers (M), to obtain a vapour (V) containing said monomers (M); b. Condensing at least a portion of the monomers (M) by contacting the vapour (V) with an aqueous solution (A) or water, to obtain a heterogeneous mixture of an organic phase containing vinylaromatic monomers (M) and an aqueous phase; c. Performing a phase separation between the organic phase and the aqueous phase; and d. Collecting the organic phase containing vinylaromatic monomers (M), to obtain the pyrolysis oil (PO) containing vinylaromatic monomers (M), wherein in step c. the aqueous phase contains at least one phosphate salt in an amount leading to a phosphate (PO4 ³ ') concentration of > 0 mol/L, preferably at least 0.01 mol/L, more preferably at least 0.1 mol/L, more preferably 0.2 to 2 mol/L, more preferably 0.4 to 1 mol/L. Preferably, the method is continuous. The at least one phosphate salt can be introduced into the aqueous solution (A) used in step b. for condensing monomers (M), or is introduced into the heterogeneous mixture between step b. and c., or in step c. after obtaining the heterogeneous mixture in step b., or a combination of these options.

The pyrolysis oil (PO) obtained from the process of the invention typically contains at least 10% by weight, often at least 40% by weight, often at least 50% by weight, in some cases at least 60% by weight, based on the total weight of the pyrolysis oil (PO), of vinylaromatic monomers (M).

The method may further comprise additional steps, wherein the pyrolysis oil (PO) or individual components thereof, such as monomers (M), are purified and/or isolated. Preferably, the method further comprises the step of distillation of the organic phase containing the pyrolysis oil (PO).

Another aspect of the present invention is a system configured for performing the method of the invention, comprising a means for carrying out a pyrolysis of a polymer (P) com- prising repeating units of vinylaromatic monomers (M), a means for quenching the pyrolysis reaction with an aqueous solution (A) or water, a means for performing phase separation, a means for collecting the organic phase from the means for performing phase separation, and a means for dosing salt, configured to dose at least one phosphate salt into the aqueous solution (A) used for quenching the pyrolysis reaction or into the means for performing phase separation, and optionally a distillation means.

The use of an aqueous solution containing a phosphate salt in an amount leading to a phosphate (PC>4 ³ ') concentration of > 0 mol/L preferably at least 0.01 mol/L, more preferably at least 0.1 mol/L, more preferably 0.2 to 2 mol/L, more preferably 0.4 to 1 mol/L for quenching a pyrolysis reaction for the recovery of vinylaromatic monomers (M) from a polymer (P) comprising repeating units of said vinylaromatic monomers (M), is another aspect of the present invention.

Moreover, an aspect of the present invention is a method for increasing the speed of phase separation of a heterogeneous liquid mixture comprising vinylaromatic monomers (M) obtained from pyrolysis of a polymer (P), and an aqueous solution (A) or water, wherein the process comprises the step of adjusting the amount of phosphate ions in the aqueous phase of the heterogeneous mixture to a concentration of at least 0.01 mol/L, preferably of at least 0.1 mol/L, more preferably 0.2 to 2 mol/L, more preferably 0.4 to 1 mol/L.

Yet another aspect of the present invention is a heterogeneous liquid mixture comprising an organic phase comprising vinylaromatic monomers (M) obtained from pyrolysis of a polymer (P), and an aqueous phase comprising at least one phosphate salt in an amount leading to a phosphate (PC>4 ³ ') concentration of at least 0.01 mol/L, preferably of at least 0.1 mol/L, more preferably 0.2 to 2 mol/L, more preferably 0.4 to 1 mol/L.

Another aspect of the invention is the use of an aqueous solution (A) containing a phosphate salt in an amount leading to a phosphate (PC>4 ³ ') concentration of > 0 mol/L preferably at least 0.01 mol/L, more preferably at least 0.1 mol/L, more preferably 0.2 to 2 mol/L, more preferably 0.4 to 1 mol/L, for washing a pyrolysis oil (PO) containing vinylaromatic monomers (M) obtained from pyrolysis of a polymer (P) comprising repeating units of said monomers (M).

The invention and the components used therein are discussed below in more detail. The terms “pyrolysis” and “depolymerization”, in the present context are understood as synonyms, and refer to the at least partial decomposition, preferably thermal decomposition, optionally in the presence of catalysts, of a polymer, yielding the monomers from which it was prepared.

The vinylaromatic monomers (M) may be any vinylaromatic monomers, such as styrene, alpha-methyl styrene, and other substituted styrenes. Preferably, the vinylaromatic monomers (M) comprise, more preferably consist of, styrene. The terms “monomers (M)” and “vinylaromatic monomers (M)” are to be understood as synonyms, as long as “(M)” is present.

The polymer (P), from which the monomers (M) are obtained, may be any polymer comprising repeating units of said monomers (M), which can be subjected to pyrolysis, in order to obtain the monomers (M). The term “polymer” includes both homopolymers of monomers (M) or copolymers of monomers (M) with one or more other monomers. Preferably, the polymer (P) originates from polymer waste, more preferably post-consumer polymer waste.

Step a.

Step a. of the inventive method comprises the pyrolysis of the polymer (P) comprising repeating units of vinylaromatic monomers (M), preferably styrene. The polymer (P) as such may be subjected to pyrolysis, or it may be subjected to pyrolysis as part of a composition. For example, if polymer (P) originates from polymer waste, preferably postconsumer polymer waste, it may be isolated from the polymer waste before pyrolysis, or the polymer waste as such may be subjected to pyrolysis. Preferably, the polymer (P) or the composition (preferably polymer waste) comprising polymer (P) is provided as a continuous stream into the pyrolysis reactor.

The composition comprising polymer (P) may further comprise other components, e.g. other polymeric materials, free monomers (M), oligomers thereof, decomposition products of polymer (P) and additives. Preferably, the total amount of bound vinylaromatic monomers in the composition (i.e. repeating units of the vinylaromatic monomers (M) in the polymer (P), in oligomers and co-oligomers of the vinylaromtic monomers (M)), constitutes at least 15 wt.%, more preferably at least 20 wt.%, more preferably at least 40 wt.%, more preferably at least 60 wt.%, based on the total weight of the composition.

In some embodiments, the composition comprising polymer (P) is post-consumer waste comprising from 75 to 95% by weight, preferably from 80 to 90% by weight, based on a total weight of the post-consumer waste, of bound vinylaromatic monomers (M) in the form of repeating units of at least one polymer (P) and oligomers of the vinylaromatic monomers (M).

The amount of vinylaromatic monomers (M) in the pyrolysis oil (PO) obtained from the process of the invention will generally depend on the amount of repeating units of said vinylaromatic monomers (M) in the polymer (P) and on the amount of free vinylaromatic monomers (M) in the composition comprising the polymer (P) that is subjected to the pyrolysis of step a.. Typically, the amount of vinylaromatic monomers (M) in the pyrolysis oil (PO) is in the range of 60 to 80% by weight, often 65 to 75% by weight, based on the amount of bound vinylaromatic monomers (M) in the composition subjected to the pyrolysis of step a..

Furthermore, the composition may comprise monomers other than vinylaromatic monomers (M), oligomers of such monomers and/or co-oligomers of such monomers, preferably co-oligomers of such monomers with vinylaromatic monomers (M). Such other monomers are often selected from the group consisting of ethylene, alpha-olefins such as 1- propylene or 1 -butylene, alkyl acrylates such as butyl acrylate, alkyl methacrylates, such as methyl methacrylate, dienes such as butadiene or isoprene, acrylonitrile, methacrylonitrile and vinyl chloride. Preferably, such other monomers, if present, are selected from the group consisting of butyl methacrylate, methyl methacrylate, acrylonitrile and butadiene. More preferably, such other monomers are selected from the group consisting of butyl methacrylate, acrylonitrile and butadiene.

Other components that may be present in the composition comprising polymer (P) are auxiliaries, additives and/or impurities, e.g. water, halogenated substances, inorganic or organic dyes or pigments, lubricants, waxes, amides of long chain organic acids, emulsifiers, soaps, paper, cardboard, metals, metal oxides, metal salts, fillers, and other additives such as UV stabilizers, hindered amine light stabilizers (HALS), hindered phenols, disulfite stabilizers, quenchers and absorbers.

The polymer (P) may be a polymer containing only repeating units derived from vinylaromatic monomers (M), preferably styrene, or a polymer containing repeating units derived from vinylaromatic monomers (M), preferably styrene, and repeating units derived from other monomers, such as the monomers listed above. Preferably, the polymer (P) comprises one or more polymers selected from the group consisting of polystyrene (PS), such as general purpose polystyrene (GPPS) or high impact polystyrene (HIPS), styrene acrylonitrile copolymers (SAN), acrylonitrile-styrene-acrylate copolymers (ASA), acrylo- nitrile-butadiene-styrene copolymers (ABS), styrene-butadiene-copolymers (SBC), sty- rene-isoprene copolymers (SIC), styrene-butadiene rubbers (SBR) and styrene-methyl methacrylate copolymers (SMMA). More preferably, the polymer (P) comprises one or more polymers selected from the group consisting of PS, HIPS, ASA, ABS and SBC.

Preferably, the polymer (P) comprises 30 to 100% by weight, more preferably 50 to 100% by weight, more preferably 60 to 100% by weight, more preferably 70 to 100% by weight, based on the total weight of polymer (P), of repeating units derived from vinyl aromatic monomers (M), preferably styrene or alpha-methylstyrene, more preferably styrene, and optionally 0 to 70% by weight, preferably 0 to 50% by weight, more preferably 0 to 40% by weight, more preferably 0 to 30% by weight, based on the total weight of polymer (P), of co-monomers, preferably selected from the group consisting of ethylene, alpha-olefins such as 1 -propylene or 1 -butylene, alkyl acrylates such as butyl acrylate, alkyl methacrylates, such as methyl methacrylate, dienes such as butadiene or isoprene, acrylonitrile, methacrylonitrile and vinyl chloride, more preferably selected from the group consisting of butyl methacrylate, methyl methacrylate, acrylonitrile and butadiene, more preferably selected from the group consisting of butyl methacrylate, acrylonitrile and butadiene.

Furthermore, when provided as part of a composition or polymer waste comprising polymer (P), the polymer (P) is preferably present in the composition or polymer waste in an amount of 30 to 100% by weight, more preferably 50 to 99.9% by weight, more preferably 60 to 99% by weight, more preferably 80 to 95% by weight, based on the total weight of the composition or polymer waste.

The pyrolysis of the polymer (P) may be carried out by any means known in the art. For example, the pyrolysis may be carried out in a fluidized bed reactor, tube reactor, tube bundle reactor, stirred tank reactor, extruder, or rotary kiln reactor. Preferably, the pyrolysis is carried out continuously, in a reactor allowing continuous pyrolysis, e.g. a fluidized bed reactor, tube reactor, tube bundle reactor, continuous stirred tank reactor, extruder or rotary kiln reactor.

Furthermore, the pyrolysis may be carried out under any conditions suitable for pyrolysis. Preferably, the pyrolysis is carried out at a temperature of from 350 to 1000 °C, preferably 400 to 900 °C, more preferably 500 to 800 °C, more preferably 550 to 650 °C, more preferably 580 to 630 °C. Furthermore, preferably the pyrolysis is carried out with an average residence time of the styrene-containing polymer waste stream in the reactor of from 0.1 second to 10 minutes, preferably from 0.2 seconds to 60 seconds, more preferably from 0.3 seconds to 10 seconds.

Other suitable conditions for pyrolysis are described, e.g. in W02021/053074, W02021/053075 and W02021/074112. A vapour (V) containing vinylaromatic monomers (M) and other components is obtained from the pyrolysis of the polymer (P) in step a. Where the vinylaromatic monomers (M) are styrene, the vapour (V) can be referred to as crude styrene gas (CSG).

For example, step a. may comprise following stages: a1. providing a composition, preferably polymer waste, more preferably post-consumer polymer waste, comprising

30 to 100% by weight, preferably 50 to 99.9% by weight, more preferably 60 to 99% by weight, more preferably 80 to 95% by weight, based on the total weight of the composition, of at least one polymer (P) containing repeating units of vinylaromatic monomers (M);

0 to 60% by weight, preferably 0 to 45% by weight, more preferably 0 to 37% by weight, more preferably 0 to 18% by weight, based on the total weight of the composition, of polyolefins and/or polyalkyl(meth)acrylates;

0 to 10% by weight, preferably 0 to 5% by weight, more preferably 0 to 3% by weight, more preferably 0 to 2% by weight, of other polymeric materials; and 0 to 40% by weight, preferably 0.1 to 35% by weight, more preferably 1 to 30% by weight, more preferably 5 to 20% by weight, based on the total weight of the composition, of additives and non-polymeric components; a2. continuously feeding the composition provided in step a1. to the reaction zone of a pyrolysis reactor wherein the pyrolysis temperature is set to a value of from 350 to 1000 °C, preferably 400 to 900 °C, more preferably 500 to 800 °C, more preferably 550 to 650 °C, more preferably 580 to 630 °C and wherein the residence time of the composition in the reaction zone is set to a value of from 0.1 second to 10 minutes, preferably from 0.2 seconds to 60 seconds, more preferably from 0.3 seconds to 10 seconds, in order to conduct pyrolysis of the polymer (P) and other pyrolyzable components of the composition, and to obtain a vapour (V) containing vinylaromatic monomers (M); a3. continuously withdrawing the vapour (V) containing vinylyromatic monomers (M) from the reaction zone of the pyrolysis reactor.

Step b.

Step b. comprises the condensation of at least a portion of the monomers (M) from the vapour (V) by contacting the vapour (V) with an aqueous solution (A) or water. This leads to the termination of the radical pyrolysis reaction, and is also known as “quenching” of the reaction with the aqueous solution. Quenching induces the condensation of vinylaromatic monomers (M) and other condensable components present in the vapour (V), and transfers them to a liquid state. I.e. step b. includes both quenching and condensing. The term “aqueous solution” in the context of the present invention relates to a homogeneous solution of any substance in water.

In one embodiment, using an aqueous solution (A) containing a phosphate salt for quenching the pyrolysis is preferable, since an additional step of adding a phosphate salt to the aqueous phase in step c. may be omitted. In another embodiment, it is preferable to add the phosphate afterwards in step c., between steps b. and c. or to apply a combination thereof. In yet another embodiment, the phosphate salt is added to the aqueous solution (A) used for quenching, and also added in step c. and/or between steps b. and c..

Where the quenching is carried out with an aqueous solution (A) of a phosphate salt, the aqueous solution (A) contains at least one phosphate salt in an amount leading to a phosphate (PC>4 ³ ') concentration of > 0 mol/L, preferably at least 0.01 mol/L, more preferably at least 0.1 mol/L, more preferably 0.2 to 2 mol/L, more preferably 0.4 to 1 mol/L.

Quenching may be carried out by any suitable means known in the art, which involve direct contact of the vapour (V) comprising the pyrolysis products with an aqueous solution (A) or water. For example, quenching may be carried out by transferring the vapour (V) into a condensation vessel and introducing, preferably spraying, the aqueous solution (A) or water into the condensation vessel. Quenching may also be carried out by introducing the pyrolysis vapour (V) into the aqueous solution (A) or water (“bubbling”) contained in a quenching vessel. Where quenching is carried out by introducing the pyrolysis vapour (V) into the aqueous solution (A) or water, it is often useful to lead the vapour (V) through a fine mesh, e.g. a glass frit, in order to decrease the size of bubbles, and thus increase the area of contact between the vapour (V) and the aqueous solution (A) or water.

Preferably, the conditions of quenching are selected thus that at least 60% by weight, more preferably at least 80% by weight, more preferably at least 90% by weight, more preferably at least 99% by weight of the vinylaromatic monomers (M) present in vapour (V) are condensed. This may be achieved, e.g., by selecting an appropriate temperature of the aqueous solution (A).

Preferably, the temperature of the aqueous solution (A) or water is set to a value of from -20 to 50 °C, more preferably from 5 to 40 °C, more preferably from 10 to 35 °C.

A heterogeneous liquid mixture of an organic phase, comprising vinylaromatic monomers (M), and an aqueous phase is obtained from the quenching of the pyrolysis reaction in step b. Step c.

Step c. comprises performing a phase separation between the organic phase comprising vinylaromatic monomers (M) and the aqueous phase.

To perform the inventive method, the phase separation between the organic phase and the aqueous phase must be carried out thus that the aqueous phase contains at least one phosphate salt in an amount leading to a phosphate (PC>4 ³ ') concentration of > 0 mol/L, preferably at least 0.01 mol/L, more preferably at least 0.1 mol/L, more preferably 0.2 to 2 mol/L, more preferably 0.4 to 1 mol/L.

Accordingly, where an aqueous solution (A) not containing any phosphate salts or at a too low concentration, or demineralized water was used for quenching in step b., at least one phosphate salt is added to the heterogeneous mixture obtained from step b. to adjust the phosphate (PC>4 ³ ') concentration to > 0 mol/L, preferably at least 0.01 mol/L, more preferably at least 0.1 mol/L, more preferably 0.2 to 2 mol/L, more preferably 0.4 to 1 mol/L, before phase separation in step c. is carried out. The phosphate salt may be provided as a solid, or may be dissolved prior to addition.

In contrast, in some embodiments where an aqueous solution (A) comprising a phosphate salt was used for quenching in step b., the addition of a phosphate salt in the phase separation step c. can be omitted. However, the phosphate may also be added between steps b. and c., or by applying a combination of an addition at said steps.

The phase separation between the organic and the aqueous phase may be carried out under any suitable conditions, at which the organic and aqueous phases are in the liquid state. Preferably, the phase separation is carried out at ambient pressure at 5 to 60 °C, more preferably at 10 to 50 °C, more preferably at 15 to 40 °C.

Furthermore, the phase separation may be carried out by any means known in the art for this purpose. For example, phase separation may be carried out directly in the vessel used for quenching.

Alternatively, the heterogeneous mixture may be transferred into a separate vessel, e.g. a separating funnel or a phase separator, where the phase separation is carried out. In continuous processes, the heterogeneous mixture obtained from step b. may e.g. be continuously transferred into a vessel (if required together with a stream of one or more phosphate salts) where the organic phase may be continuously withdrawn from the top of the vessel and the aqueous phase may be continuously withdrawn from the bottom of the vessel, while the mixed phase is continuously provided in the center of the vessel. In cases where the organic phase contains a large amount of high-density organic components (e.g. halogenated organic components, such as halogenated vinylaromatic monomers), the withdrawal of the aqueous phase may also be carried out at the top of the vessel, while the withdrawal of the organic phase is carried out at the bottom of the vessel. Where the organic phase is rich in styrene or low-density components, the organic phase is typically withdrawn from the top of the vessel.

When performing the phase separation of step c., the volume ratio of organic phase to the aqueous phase may for example be from 95:5 to 5:95, preferably from 80:20 to 10:90, more preferably from 50:50 to 20:80, more preferably from 40:60 to 25:75. The ratio may e.g. be adjusted by regulating the amount of aqueous solution (A) or water used in step b. or by adding and withdrawing aqueous solution in step c..

In order to perform the method of the invention, the aqueous phase comprises a phosphate salt in an amount leading to a phosphate (PC>4 ³ ') concentration > 0 mol/L. Preferably the amount of phosphate salt is selected such that the concentration of phosphate ions PO4 ³ ; is at least 0.01 mol/L, more preferably at least 0.1 mol/L, more preferably 0.2 to 2 mol/L, more preferably 0.4 to 1 mol/L.

The phosphate salt used in the inventive method may be any phosphate salt with sufficient solubility in water to obtain the above concentrations. Preferably the salt is selected from alkali metal phosphates, alkali metal phosphate hydrates, ammonium phosphates, ammonium phosphate hydrates, and mixtures thereof, preferably selected from the group consisting of Na _n H3-nPC>4, Knh -nPCL, (NhDnHs-nPCL, and their hydrates, wherein n is an integer from 1 to 3, and mixtures thereof, more preferably selected from NasPCL, K3PO4, (NH ₄ ) ₃ PO ₄ , and their hydrates, and mixtures thereof, more preferably selected from NasPCL, K3PO4 and mixtures thereof, more preferably K3PO4.

Step d.

In step d., the organic phase containing vinylaromatic monomers (M) is collected from the phase-separated heterogeneous mixture, to obtain the pyrolysis oil (PO) containing vinylaromatic monomers (M).

The collecting may be carried out by any suitable means known in the art. For example, where a separating funnel was used for phase separation, if the organic phase has a lower density than the aqueous phase, the aqueous phase can be released from the bottom of the separating funnel, while the organic phase comprising vinylaromatic monomers (M) is collected in the separating funnel. If the organic phase has a higher density than the aqueous phase (e.g. when halogenated organic compounds such as halogenated vinylaromatic monomers are present), the organic phase may be released from the bottom of the separating funnel and collected in a separate vessel, whereas the aqueous phase may remain in the separating funnel.

Alternatively, if the organic phase has a lower density than the aqueous phase, the organic phase comprising vinylaromatic monomers (M) may be siphoned from the top of the phase-separated heterogeneous mixture and be collected in a separate vessel, whereas the aqueous phase may remains in the vessel used for phase separation. If the organic phase has a higher density than the aqueous phase (e.g. when halogenated organic compounds such as halogenated vinylaromatic monomers are present), the organic phase may be collected in the vessel used for phase separation, whereas the aqueous phase us siphoned from the top.

In continuous processes, if the organic phase has a lower density than the aqueous phase, the organic phase may e.g. be continuously withdrawn from the top of the vessel, wherein phase separation of step c. took place, and further be collected in a separate vessel, e.g. in a storage tank, whereas the aqueous phase may be continuously withdrawn from the bottom of the vessel. If the organic phase has a higher density than the aqueous phase (e.g. when halogenated organic compounds such as halogenated vinylaromatic monomers are present), the organic phase may e.g. be continuously withdrawn from the bottom of the vessel, wherein phase separation of step c. took place, and further be collected in a separate vessel, e.g. in a storage tank, whereas the aqueous phase may be continuously withdrawn from the top of the vessel.

Preferably, simultaneously with the collection of the organic phase, the aqueous phase is also collected and further recycled for use in the quenching step b.

In addition to the above steps a. to d., the pyrolysis oil (PO) containing vinylaromatic monomers (M) obtained from step d. may further be processed, in order to purify and/or isolate the pyrolysis oil (PO) or its individual components, such as the vinylaromatic monomers (M), preferably styrene and/or alpha-methylstyrene, in particular styrene, and optionally side products, e.g. ethylbenzene or toluene. Preferably, the pyrolysis oil (PO) is further processed by distillation, more preferably fractional distillation.

In continuous processes, the pyrolysis oil (PO) may e.g. be fed into a fractional distillation column, where it is fractionally distilled to obtain fractions enriched with individual components of the pyrolysis oil (PO), preferably at least one fraction enriched with vinylaromatic monomers (M), in particular styrene. In some embodiments, a multitude of distillation steps can be performed in order to obtain components of high purity, e.g. at least 99 % by weight. In addition or alternatively, purification of the pyrolysis oil (PO) can involve crystallization, e.g. fractional crystallization, by means known in the art. The pyrolysis oil (PO) obtained from the process of the invention typically contains at least 10 wt.-%, often at least 40 wt.%, often at least 50 wt.%, in some cases at least 60% by weight, based on the total weight of the pyrolysis oil (PO), of vinylaromatic monomers (M), in particular styrene.

In a preferred embodiment, the steps of phase separation (step c.), collection (step d.) and optional distillation are carried out until the produced pyrolysis oil (PO), obtained by performing the method of the invention, contains at least 70 wt.% of vinylaromatic monomers (M), in particular styrene. In another embodiment the steps are carried out until the mixture of vinylaromatic monomers (M), in the produced pyrolysis oil (PO), obtained by performing the inventive method, contains at least 50 wt.%, preferably at least 70 wt.%, based on the mixture of vinylaromatic monomers (M), of styrene.

Another aspect of the disclosed invention is a system configured for performing the inventive method for the recovery or recycling of vinylaromatic monomers (M), in particular styrene, from a polymer (P) as described above, or a composition comprising polymer (P). The device comprises a means for carrying out a pyrolysis of a polymer (P) comprising repeating units of vinylaromatic monomers (M), a means for quenching the pyrolysis reaction with an aqueous solution (A) or water, a means for performing phase separation, a means for collecting the organic phase from the means for performing phase separation, and a means for dosing salt, configured to dose at least one phosphate salt into the aqueous solution (A) used for quenching the pyrolysis reaction or into the means for performing phase separation. Preferably, the system further comprises a distillation means. The means for carrying out the individual steps are preferably those described above for the individual steps.

The invention is further illustrated by the following examples, Figures and claims.

Fig. 1 shows a graph of phase separation over time in heterogeneous mixtures of pyrolysis oil and aqueous solutions of K3PO4 with different concentrations from 0 to 1 M, as measured in Example B.

Fig. 2 shows a graph of phase separation after 5 min for heterogeneous mixtures of pyrolysis oil and aqueous solutions of K3PO4 with different concentrations from 0 to 1 M, as measured in Example B.

Fig. 3 shows a graph of the reproducibility of phase separation for concentrations of 0.1 M and 0.4 M, as measured in Example B.

Fig. 4 shows a graph comparing phase separation using NasPO4 and K3PO4, as examined in Example C.

Fig. 5 shows the setup for a pyrolysis process as described in Example D. Examples

The examples were carried out using pyrolysis oil (PO) obtained from a standard pyrolysis process of post-consumer waste containing 85 wt% of bound styrene monomers in the polymer chains. The aqueous solutions were based on demineralized water, wherein different amounts of salts were dissolved.

An experimental set-up was installed to allow for the monitoring of the described separation of layers during the phase separation process via camera. A measuring ruler was placed vertically next to the glass vial to allow for a quantification of the phase separation degree in a function of time.

A glass vial was successively filled with demineralized water or an aqueous solution containing K3PO4, NasPOt or KCI in a specific quantity, and the pyrolysis oil (PO). Aqueous solutions were obtained by dissolving the corresponding solid salts in demineralized water. (K3PO4 3H2O and Na3PO4' 12H2O were used to prepare K3PO4 and NasPO4 solutions, respectively. The water presence in these solids was taken into consideration when determining the concentration of the obtained solutions.)

For the experiment, the oil was added slowly into the glass vial via syringe against the inner wall of the vial, so as not to upset the obtained two-layer-system. The glass vial was then sealed with an aluminium crimp cap and placed into the experimental setup.

A first photograph was taken to determine the original height of the contact line between both layers. The vial was then vigorously shaken by hand for 5 s, resulting in a heterogeneous emulsion, and was immediately placed in the setup after which a video recording was started. After 5 min, the recording was stopped, and a second photograph was taken with additional lighting to show a possible emulsion more clearly.

The obtained phase separation was quantified as follows: During phase separation, a homogeneous aqueous fraction appears, starting at the bottom of the glass vial.

As the emulsion is gradually broken up, this layer rises from the bottom (0 %) to the height of the original contact line before mixing (100 %). At complete (100 %) phase separation, the original height is reached, while a partial separation (between 0 % and 100 %) reaches a height between the bottom of the glass vial and the original height.

When performing the experiments, it has to be taken into account that phase separation depends on many factors. E.g., phase separation time depends on the geometry of the container, where a bigger interface surface usually phase separates faster than a smaller interface surface. In addition, the amount of aqueous phase and the amount of organic phase, i.e. the ratio of the two phases, influences the progress of phase separation. More water allows more emulsion formation and thus, generates longer distances of the emulsion to phase separate, whereas a higher amount of organic phase allows deeper infusion into the aqueous phase during mixing. Therefore, the same vials were used for all experiments, and the same volume ratios of pyrolysis oil (PO) and aqueous solution were employed. The effects shown in the examples are observed for other configurations, provided the vials and ratios in the comparative examples are the same as in the examples according to the invention. Hence relative comparison is allowed.

Example A

In a first approach, one type of glass vial was chosen and the influence of the ratio between aqueous phase and pyrolysis oil (PO) on phase separation within a 5 min timeframe was observed. 15 mL aqueous solution (demineralized water or 1 M K3PO4 solution; 1 M = 1 mol/L) and 5 to 15 mL PO were filled into a glass vial of 50 mL (internal diameter = 28.6 mm), mixed for 5 s and then allowed to phase separate for 5 min at room temperature (20 °C).

Table 1 :

Phase separation between PO and aqueous phase in different ratios after 5 min volume [mL] phase separation af- comnosition

PO aqueous solution ter 5 min [%]

1 15 15 demineralized water 0

2 15 15 1 mol/L K3PO4 8.0

3 7.5 15 demineralized water 0

4 7.5 15 1 mol/L K3PO4 98.0

5 5 15 demineralized water 0

6 5 15 1 mol/L K3PO4 100.0

While in mixtures with demineralized water no phase separation occurred during the observation time of 5 min (and even not after 24 hours, not shown in tables), immediate phase separation up to 100 % after 5 min was measured with K3PO4 aqueous solution. Upon these results, a volume of 5 mL PO and 15 mL aqueous solution, i. e. a ratio of 1 :3, was selected for further experiments to allow evaluation of the enhanced phase separation effect within the observation time of 5 min.

Example B The mixture of demineralized water and PO after shaking does not separate into two distinct layers over a period of 5 min but forms one overall phase, a heterogeneous emulsion. It was found that the presence of phosphate ions enhances the rate of phase separation. Hence, in a second approach, the effect of increasing the PC>4 ³ ' concentration in the aqueous layer on phase separation was analysed. The experiment was conducted as outlined above: 5 mL PO and 15 mL aqueous solution with various concentrations of K3PO4 were mixed for 5 s and then, phase separation at room temperature was observed for 5 min. Measurements were taken at several time points after mixing (table 2, after 2.5 and 5 min; Fig. 1 , every 30 s from 0.5 to 5 min). The results are shown in Table 2 and Fig. 1. Fig. 2 presents the dependency of phase separation [%] after 5 min on the concentration of the K3PO4 aqueous solution; concentrations vary from 0 to 1 mol/L of K3PO4.

Table 2: phase separation between CSO and aqueous phase with different concentrations Of K3PO4 phase separation [%] concentration - type of example aqueous solution after after 5 min

[mol/L] .

2.5 mm comparative demineralized wa- 0 0 ter

7 inventive K3PO4 0.01 14.6 25.0

8 inventive K3PO4 0.04 20.8 43.8

9 inventive K3PO4 0.06 29.2 54.2

10 inventive K3PO4 0.08 31.3 58.3

11 inventive K3PO4 0.10 42.9 77.6

12 inventive K3PO4 0.15 50.0 87.5

13 inventive K3PO4 0.20 85.7 95.5

14 inventive K3PO4 0.40 85.4 100.0

15 inventive K3PO4 0.60 89.6 100.0

16 inventive K3PO4 0.80 87.8 100.0

6 inventive K3PO4 1.00 89.8 100.0

The results clearly demonstrate the beneficial effect of K3PO4 in the aqueous layer to increase the rate of phase separation between PO and the aqueous solution. A saturation of the effect is reached as from a concentration of approximately 0.4 mol/L K3PO4 in the aqueous solution.

To confirm the findings of the experiment, measurements were repeated several times. All results showed good reproducibility as shown in Fig. 3 and listed in Table 3 for concentrations of 0.1 and 0.4 mol/L K3PO4. Table 3: reproducibility of phase separation between CSO and aqueous phase with 0.1 or 0.4 mol/L K3PO4 phase separation [%] concentration - type of example aqueous solution after after 5 min

[mol/L] .

2.5 mm

11 inventive K3PO4 0.10 42.9 77.6

17 inventive K3PO4 0.10 42.9 77.6

18 inventive K3PO4 0.10 41.7 79.2

14 inventive K3PO4 0.40 85.4 100.0

19 inventive K3PO4 0.40 87.8 100.0

20 inventive K3PO4 0.40 85.7 100.0

Example C

In further approaches, others salt solutions were tested in the same setup, in order to confirm that the active ingredient of the fast-separating mixture is indeed the phosphate (PO4- ³ "). The faster phase separation could either be caused by the anionic PC>4 ³ ' (phosphate) ions or the cationic K ⁺ ions of the K3PO4. Therefore, the experimental result was compared both to NasPO4 and to KCI as ingredients in the aqueous solution. The previously used 0.10 M and 0.40 M K3PO4 solutions were chosen as reference.

In case of the use of KCI aqueous solutions, concentrations of 0.30 M and 1.2 M were employed, in order to establish the same K ⁺ ion concentration as in the 0.10 M and 0.4 M K3PO4 solutions, respectively.

Measurements according to the experimental setup were not possible, as during the observation a clear horizontal interface between the layers was not formed. Even though some separation occurred, it could rather be described as an emulsion of larger PO droplets in the aqueous solution. This leads to the conclusion that the effect described above is not caused by the K ⁺ ions.

In case of the NasPO4 aqueous solution, phase separation was observed in a similar way as for K3PO4 before. In both cases, a clear horizontal interface was achieved during phase separation. This leads to the conclusion that the presence of PC>4 ³ ' ions is responsible for the improved and accelerated phase separation, and the cation can be varied. The results are shown below in table 4 and in Fig. 4. Table 4: phase separation between CSO and aqueous phase with K ₃ PO ₄ or Na ₃ PO ₄ aqueous solution phase separation [%] concentration - type of example aqueous solution after after 5 min

[mol/L] .

2.5 mm

11 inventive K ₃ PO ₄ 0.10 42.9 77.6

21 inventive Na ₃ PO ₄ 0.10 63.3 83.7

14 inventive K ₃ PO ₄ 0.40 85.4 100.0

22 inventive Na ₃ PO ₄ 0.40 83.3 91.7

The above findings also show that, although the mass of the used salts, and thus the density of the aqueous solution, also may have some influence on phase separation (Na ₃ PO ₄ : 0.4 mol/L = 65.6 g/L; K ₃ PO ₄ : 0.4 mol/L = 84.9 g/L; KCI: 1.2 mol/L = 89.5 g/L), the main effect can be attributed to the presence of PO ₄ ³ ' ions.

Example D

Pyrolysis of post-consumer waste containing 85 wt% of bound styrene monomers in the polymer chains is carried out in a standard fluidizing bed reactor configured for carrying out continuous pyrolysis of polystyrene, operating at an inner temperature of 600 °C. The feeding rate of polystyrene into the pyrolysis zone of the reactor is selected to ensure an average residence time of polystyrene in the pyrolysis zone of 5 seconds. The pyrolysis vapours are transferred via a conduit into a quencher, where a 0.4 M aqueous K ₃ PO ₄ solution having a temperature of 20 °C is sprayed from the top into the condensation vessel. The condensed phase is collected at the bottom of the vessel and transferred into a phase separator. The organic phase is withdrawn from the top of the phase separator and subjected to distillation in a fractional distillation column. The aqueous phase is withdrawn from the bottom of the vessel and recycled into the condensation vessel. The setup is schematically shown in Fig. 5.