CLAIMS

1. Process (200) for treating a gaseous effluent resulting from a pyrolytic decomposition of a polymer or a mixture of polymers, making it possible to recover one or more monomer(s) contained in said gaseous effluent, said method being characterized in that it comprises the following steps:

a condensation step (210) consisting in injecting, into a condensation chamber (110) maintained under a first pressure pi, the gaseous effluent and bringing it into contact with an absorbing liquid, the temperature of said absorbing liquid being lower than the temperature of the gaseous effluent, so that the said monomer(s) condense(s) in the absorbing liquid by heat exchange,

a stage of partial vaporization (230) of the condensate obtained at the end of the condensation stage, by expansion of the condensate in an enclosure (130) maintained under a second pressure P2, lower than the first pressure pi,

a reinjection step (240) consisting in redirecting, at least in part, a first fraction, liquid or vapor, obtained at the end of the partial vaporization step (230) towards the condensation enclosure (110) to absorb again the monomer(s) contained in the gaseous effluent, and

a recovery step (250) comprising purification of a second fraction, liquid or vapor, obtained at the end of the partial vaporization step (230) and charged with monomer(s).

2 . Process according to Claim 1, characterized in that the first pressure pi is between 0.1 and 5 bars and preferably between 0.5 and 2 bars absolute.

3 . Process according to Claim 1, characterized in that the temperature of the absorbent liquid is lower by at least 50°C than the temperature of the gaseous effluent.

4. Method according to claim 1, characterized in that the temperature of the absorbent liquid is lower by at most 450° C. than the temperature of the gaseous effluent.

5. Process according to claim 1, characterized in that the temperature of the absorbing liquid is lower by at least 50° C. and by at most 450° C. than the temperature of the gaseous effluent.

6. Method according to claim 1, characterized in that the second chamber 130 is maintained at a pressure p2 of between 0.001 and 0.8 bar.

7. Method according to claim 1, characterized in that the pressure difference in absolute value between the first enclosure 110 and the second enclosure 130 is greater than or equal to 0.5 bar.

8. Method according to claim 1, characterized in that the recovery step (250) comprises a condensation of the vapor fraction obtained at the end of the partial vaporization step 230 if the second fraction loaded with monomer (s) is a vapor fraction.

9. Method according to claim 1, characterized in that the recovery step (250) comprises filtration or decantation of the liquid fraction obtained at the end of the partial vaporization step 230 if the second fraction charged with monomer (s) is a liquid fraction.

10. Method according to any one of the preceding claims, characterized in that during the reinjection step (240), the first fraction reinjected is a liquid fraction and during the recovery step (250), the second fraction recovered is a vapor fraction.

11. Method according to any one of the preceding claims, characterized in that the absorbent liquid is selected so that the ratio between its latent heat of vaporization DHn in the standard state and its molar specific heat Cp in the standard state is higher than that of the monomer(s) to be recovered.

12. Method according to any one of the preceding claims, characterized in that the absorbent liquid is chosen from one of the following compounds: benzene, benzonitrile, a compound of formula R-COOH, and a compound of formula R- OH, in which R can be chosen from alkyls, the carbon number of which is between 1 and 5, a phenyl or a hydrogen.

13. Method according to any one of the preceding claims, characterized in that the absorbent liquid is chosen from one of the following compounds: the absorbent liquid is chosen from one of the following compounds: a compound of formula R-OH, a compound of formula R—COOH, in which R can be chosen from alkyls, the number of carbons of which is between 1 and 5, or a hydrogen.

14. Method according to any one of the preceding claims, characterized in that the absorbent liquid is chosen from dihidrogen monoxide, methanol, ethanol, propanol, butanol, formic acid, acetic acid or their mixtures

15. Method according to any one of the preceding claims, characterized in that the absorbent liquid is chosen so that its boiling point is of the order of magnitude of that of the monomer(s) to be recovered ± 80 °C.

16. Method according to claim 15, characterized in that the absorbent liquid near between a boiling point higher than or substantially equal to that of the monomer(s) to be recovered and/or of the azeotrope which it forms with the monomer(s) to be recovered.

17. Process according to any one of the preceding claims, characterized in that the polymer is selected from: polyethylenes such as high-density polyethylene (HDPE) or polyethylene terephthalate (PET); a homo- and copolymer of olefins such as acrylonitrile-butadiene-styrene copolymers, styrene-butadiene-alkyl methacrylate (or SBM) copolymers; polypropylene, polybutadiene and polybutylene; acrylic homo- and copolymers and polyalkyl methacrylates such as poly(methyl methacrylate); a polyhydroxyalkanoate; homo- and copolyamides; polycarbonates; polyesters including poly(ethylene terephthalate) and poly(butylene terephthalate); polyethers such as poly(phenylene ether), poly(oxymethylene), poly(oxyethylene) or poly(ethylene glycol) and poly(oxypropylene); polystyrene; copolymers of styrene and maleic anhydride; poly(vinyl chloride); fluorinated polymers such as poly(vinylidene fluoride), polytetrafluoride of ethylene and polychlorotrifluoro-ethylene; natural or synthetic rubbers; thermoplastic polyurethanes; polyaryl ether ketones (PAEK) such as polyetheretherketone (PEEK) and polyether ketone ketone (PEKK)

; polyetherimide; polysulfone poly(phenylene sulfide)

; cellulose acetate; poly (vinyl acetate); polypropiolactone or a mixture of two or more of these polymers.

18. Process according to any one of the preceding claims, characterized in that the monomer(s) are selected from the following compounds: methyl methacrylate, methyl acrylate, ethyl acrylate, acrylic acid, acid methacrylic, styrene, crotonic acid, gamma-butyrolactone, delta-valerolactone and mixtures thereof.

19. Method according to any one of the preceding claims, characterized in that the injection of the gaseous effluent during the condensation step (210) is carried out in co-current or in counter-current to the absorbent liquid.

20. Method according to any one of the preceding claims, characterized in that it further comprises a separation step

(220) on the condensate obtained at the end of the condensation step before the partial vaporization step (230).

21. Method according to any one of the preceding claims, characterized in that it further comprises a step of adjusting the temperature (260) of the fraction redirected to the condensation enclosure (110) to again absorb the (s) monomer(s) contained in the gaseous effluent.

22. Method according to any one of the preceding claims, characterized in that at the time of the condensation step (210), additives are added to the absorbent liquid, said additives possibly being chosen from polymerization inhibitors.

23. Method according to any one of the preceding claims, characterized in that at the time of the partial vaporization step (230), additives are added to the circuit, said additives possibly being chosen from polymerization inhibitors.

24. System for treating a gaseous effluent resulting from a pyrolytic decomposition of a polymer or a mixture of polymers, making it possible to recover one or more monomer(s) contained in said gaseous effluent, said system being characterized in that it comprises:

a condensation enclosure (110) capable of being maintained under a first pressure pi, said enclosure comprising, in its side wall, a gaseous effluent inlet orifice (111) and an absorption device (112) capable of allowing said gaseous effluent to be brought into contact with an absorbent liquid whose temperature is lower than that of the gaseous effluent, said enclosure further comprising a gas outlet orifice (113) at its upper end and an orifice (114) for outlet of the condensate obtained, in its lower part,

a second enclosure (130) in fluid communication with the condensation enclosure (110) and intended to receive the condensate obtained at the end of the condensation step, said second enclosure (130) being capable of being maintained at a second pressure p2 lower than the first pressure pi, so as to cause the expansion of the condensate and its adiabatic partial vaporization,

a pump (140) for recovering a fraction from the second chamber (130) to reinject it into the first condensation chamber (110) via the absorption device (112).

25. System according to claim 24, characterized in that it further comprises a heat exchanger (131), arranged downstream of the second enclosure (130), making it possible to condense the gaseous fraction resulting from the partial vaporization provo called by the expansion of the condensate in the second chamber (130), and a purification means (150) of the constituents of said condensed gaseous fraction.

26. System according to claim 24 or 25, characterized in that it further comprises a separation device (120), arranged upstream of the second enclosure (130), preferably capable of separating compounds by filtration, decantation, centrifugation or esterification.

27. System according to one of the preceding claims, characterized in that it further comprises a heat exchanger (160) upstream of the first enclosure (110) capable of adjusting the temperature of the liquid fraction from the second enclosure. (130) before its injection into the first chamber (110)

28. System according to one of the preceding claims, characterized in that it further comprises a purification device (170), arranged downstream of the second enclosure (130), capable of purifying part of the liquid fraction from the second enclosure (130).

29. System according to one of the preceding claims, characterized in that it further comprises an injection point (116) of absorbent liquid.

30. System according to one of the preceding claims, characterized in that the first pressure pi is between 0.1 and 5 bar; and that the temperature of the absorbing liquid is lower by at least 50° C. and by at most 450° C. than the temperature of the gaseous effluent; and the second enclosure 130 is maintained at a pressure P2 of between 0.001 and 0.8 bar, the pressure difference in absolute value between the first enclosure 110 and the second enclosure 130 is greater than or equal to 0.5 bar.

METHOD FOR TREATMENT OF A GAS EFFLUENT FROM DECOMPOSITION

PYROLYTIC OF A POLYMER

[Field of invention]

The present invention relates to the field of the treatment of gaseous effluents resulting from the decomposition of polymer(s).

[002] More particularly, the invention relates to a process for treating a gas resulting from a pyrolytic decomposition of a polymer or a mixture of polymers. This process finds its application in the recycling of plastics and plastic residues generally comprising several polymers of different grades and in particular in the recycling of polymer compounds comprising a single family of polymers.

[Prior art]

[003] In 2017, hundreds of millions of tons of plastics were produced worldwide. Thus, the production and recycling of plastics easily appear as major issues from an environmental and economic point of view. It is therefore advantageous economically and from an environmental point of view to be able to depolymerize and/or crack the polymeric resin and obtain products which can be reused. Among the classic methods of recycling plastic materials, thermal pyrolysis and mechanical recycling are the most widely used.

[004] Thermal pyrolysis consists of placing the plastic object to be treated in a suitable chamber and then heating the chamber so that the heat is transferred to the object. It makes it possible to treat plastic waste and generally leads to carbonaceous residues, oil and gases which cannot be reused as such for the production of the thermoplastic polymer matrix. Such thermal decomposition processes are used in particular to decompose PMMA (polymethyl methacrylate), polystyrene or other plastic residues. In the case of the thermal decomposition of PMMA or polystyrene, it would be interesting to be able to recover the monomers. In the case of the thermal decomposition of plastic residues, it is possible to recover a mixture of products, which can be used as fuel or heating oil. The core fraction from the pyrolysis of polyolefins is, for example, rich in a cut of the naphtha type (pyrolysis gasoline), which can advantageously be used to feed a steam cracker (conventional petrochemical unit) in order to produce olefins again. In general, the gaseous effluents resulting from this thermal decomposition by pyrolysis of polymer(s) are rich in compound(s) which it is desired to recover and recycle.

[005] To isolate and recover the compounds (e.g. the monomer(s)) the gaseous effluent must be condensed. For this, a heat exchanger is conventionally used in which the gaseous effluent will circulate, so that the heat exchanger cools the gaseous effluent until a liquid fraction is produced.

[006] The product recovered at the end of this condensation is of relatively mediocre quality and requires subsequent stages of washing and then purification by distillation.

[007] The gaseous effluent resulting from the thermal decomposition of the polymer(s) is composed of light, medium and heavy molar fractions. The monomer(s) which it is desired to recover and upgrade is (are) essentially present in the average molar fraction. The applicant has therefore sought a solution which makes it possible to isolate this molar fraction of interest more effectively.

[008] Document WO 2017/179009 describes a process and a system for separating C3 hydrocarbons from a gas mixture. The separation of the components in this system is according to their boiling point, so the process and the system correspond to a distillation column.

[009] Document US 2016/145185 describes a process for recovering purified (meth)acrylic acid during the synthesis of (meth)acrylic acid. The document describes a step for purifying a compound during its synthesis process and the heating of the distillation columns.

[0010] The document US2003/028052 describes a process for absorbing and purifying acrylic acid. The process uses distillation columns.

[Technical problem]

The object of the invention is therefore to remedy at least one of the aforementioned drawbacks of the prior art.

The invention aims in particular to propose a simple and effective solution for isolating a molar fraction of interest from a gaseous effluent resulting from the thermal decomposition of a polymer or a mixture of polymer(s), in order to recover one or more compound(s) (eg monomer(s)) of improved quality.

[Brief description of the invention]

To this end, the subject of the invention is a process for treating a gaseous effluent resulting from a pyrolytic decomposition of a polymer or a mixture of polymers, making it possible to recover one or more monomer(s) contained in said gaseous effluent, said method being characterized in that it comprises the steps known living:

- a condensation step consisting in injecting, into a condensation chamber maintained under a first pressure pi, the gaseous effluent and bringing it into contact with an absorbing liquid, the temperature of said absorbing liquid being lower than the temperature of the gaseous effluent, so that the said monomer(s) condense(s) in the absorbing liquid by heat exchange,

- a step of partial vaporization of the condensate obtained at the end of the condensation step, by expansion of the condensate in an enclosure maintained under a second pressure p2, lower than the first pressure pi,

- a reinjection step consisting in redirecting, at least in part, a first fraction, liquid or vapour, obtained at the end of the partial vaporization step towards the condensation enclosure to again absorb the monomer(s) ( s) contained in the gaseous effluent, preferably if necessary the vapor fraction is recondensed before its introduction into the condensation enclosure, and

- a recovery step comprising purification of a second fraction, liquid or vapor, obtained at the end of the partial vaporization step and charged with monomer(s).

Thus, it was discovered that the condensation, by means of an absorption device making it possible to bring the gaseous effluent into contact with an absorbing liquid whose temperature is much lower than that of the effluent, followed by the partial vaporization of the condensate obtained in the presence in particular of a pressure differential, makes it possible to effectively isolate the monomer(s) contained in the gaseous effluent resulting from the decomposition of one or more polymers.

[0015] According to other optional characteristics of the method:

during the reinjection step, the first fraction reinjected is a liquid fraction and during the recovery step, the second fraction recovered is a vapor fraction;

the absorbent liquid is selected so that the ratio between its latent heat of vaporization DHn in the standard state and its molar specific heat Cp in the standard state is greater than that of the monomer(s) to be recovered;

the absorbent liquid is chosen from one of the following compounds: benzene, benzonitrile, a compound of formula R-COOH, and a compound of formula R-OH, in which R can be chosen from alkyls, the number of carbon is between 1 and 5, a phenyl or a hydrogen;

the absorbent liquid is chosen so that its boiling point is of the order of magnitude of that of the monomer(s) to be recovered ± 80°C, preferably ± 50°C, more preferably ± 30°C and even more preferably ±10°C;

the absorbent liquid has a boiling point higher than or substantially equal to that of the monomer(s) to be recovered and/or of the azeotrope which it forms with the monomer(s) to be recovered; the polymer is selected from: polyethylenes such as high density polyethylene (HDPE) or polyethylene terephthalate (PET); a homo- and copolymer of olefins such as acrylonitrile-butadiene-styrene copolymers, styrene-butadiene-alkyl methacrylate (or SBM) copolymers; the

polypropylene, polybutadiene and polybutylene; acrylic homo- and copolymers and polyalkyl methacrylates such as poly(methyl methacrylate); a polyhydroxyalkanoate; homo- and copolyamides; polycarbonates; polyesters including poly(ethylene terephthalate) and poly(butylene terephthalate); polyethers such as poly(phenylene ether), poly(oxymethylene), poly(oxyethylene) or poly(ethylene glycol) and poly(oxypropylene); polystyrene; copolymers of styrene and maleic anhydride; poly(vinyl chloride); fluorinated polymers such as poly(vinylidene fluoride), polytetrafluoride of ethylene and polychlorotrifluoro-ethylene; natural or synthetic rubbers; thermoplastic polyurethanes; polyaryl ether ketones (PAEK) such as polyetheretherketone (PEEK) and polyether ketone ketone (PEKK); polyetherimide; polysulfone poly(phenylene sulfide); cellulose acetate; poly(vinyl acetate) or a mixture of two or more of these polymers

the monomer(s) are selected from the following compounds: methyl methacrylate, methyl acrylate, ethyl acrylate, acrylic acid, methacrylic acid, styrene, crotonic acid, gamma-butyrolactone, delta-valerolactone and their mixtures.

the injection of the gaseous effluent during the condensation step is carried out cocurrently or countercurrently to the absorbing liquid;

the method further comprises a separation step on the condensate obtained at the end of the condensation step before the partial vaporization step;

the method further comprises a step of adjusting the temperature of the fraction redirected to the condensation enclosure to absorb again the monomer(s) contained in the gaseous effluent; This step may for example include heating or cooling.

at the time of the condensation step, additives are added to the absorbent liquid, said additives possibly being chosen from polymerization inhibitors;

at the time of the partial vaporization step, additives are added to the circuit, said additives possibly being chosen from polymerization inhibitors.

The invention further relates to a system for treating a gaseous effluent resulting from a pyrolytic decomposition of a polymer or a mixture of polymers, making it possible to recover one or more monomer(s) contained ( s) in said gaseous effluent, said system being characterized in that it comprises:

a condensation enclosure capable of being maintained under a first pressure pi, said enclosure comprising, in its side wall, a gaseous effluent inlet port and an absorption device capable of allowing said gaseous effluent to come into contact with an absorbent liquid whose temperature is lower than that of the gaseous effluent, said enclosure further comprising a gas outlet orifice at its upper end and an outlet orifice for the condensate obtained, in its lower part,

a second enclosure in fluid communication with the condensation enclosure and intended to receive the liquid containing the condensate obtained at the end of the condensation step, said second enclosure being capable of being maintained at a second pressure p2 lower than the first pressure pi, so as to cause the expansion of the condensate and its adiabatic partial vaporization,

a pump making it possible to recover a liquid fraction from the second enclosure in order to reinject it into the first condensation enclosure via the absorption device.

[0017] According to other optional features of the system:

it further comprises a heat exchanger, arranged downstream of the second enclosure, making it possible to condense the gaseous fraction resulting from the partial vaporization caused by the expansion of the condensate in the second enclosure, and a means for purifying the constituents of said gaseous fraction condensed;

it further comprises a separation device, arranged upstream of the second chamber, preferably capable of separating compounds by filtration, decantation, centrifugation or esterification;

it further comprises a heat exchanger upstream of the first chamber able to adjust the temperature of, preferably to cool, the liquid fraction coming from the second chamber before it is injected into the first chamber;

it further comprises a purification device, disposed downstream of the second enclosure, capable of purifying part of the liquid fraction from the second enclosure;

it further comprises an absorbent liquid injection point.

Other advantages and characteristics of the invention will appear on reading the following description given by way of illustrative and non-limiting example, with reference to the appended Figures which represent:

• Figure 1, a block view of an example of a method according to the invention,

• Figure 2, a block diagram of an example of a system according to the invention.

[Detailed description of the invention]

[0019] In the remainder of the description, the term “monomer” is understood to mean a molecule which can undergo polymerization. The term “monomer” is understood to mean the most important monomer unit constituting a polymer. Thus, in PMMA, the monomer is Methyl MethAcrylate (MAM) whereas it is styrene for polystyrene.

[0020] The term “polymerization” as used relates to the process of transforming a monomer or a mixture of monomers into a polymer.

The term "depolymerization" as used relates to the process of converting a polymer into one or more monomer(s) and/or oligomer(s) and/or polymer(s) of smaller molar mass than the original polymer.

[0022] The expression “pyrolytic decomposition” corresponds within the meaning of the invention to a very high temperature rise step resulting in a transformation of a polymer into different compounds including monomers.

The term “polymer” is understood to mean either a copolymer or a homopolymer. A “copolymer” is a polymer grouping together several different monomer units and a “homopolymer” is a polymer grouping together identical monomer units.

[0024] The term “thermoplastic polymer” is understood to mean a polymer which, repeatedly, can be softened or melted under the action of heat and which adopts new shapes by the application of heat and pressure. Examples of thermoplastics are, for example: polyethylene, a (meth)acrylic polymer such as poly(methyl methacrylate) (PMMA), or polystyrene (PS), polyLactic acid (PLA), polyhydric oxyalkanoates (PHA).

The term “(meth)acrylic polymer” means a homopolymer or a copolymer based on (meth)acrylic monomer, which is for example chosen from methyl methacrylate, ethyl methacrylate, methyl acrylate , ethyl acrylate, methacrylic acid, acrylic acid, n-butyl acrylate, isobutyl acrylate, n-butyl methacrylate, isobutyl methacrylate, cyclohexyl, cyclohexyl methacrylate, isobornyl acrylate, isobornyl methacrylate and mixtures thereof. Poly(methyl methacrylate) (PMMA) is a particular example of a (methacrylic) polymer obtained by polymerization of a methyl methacrylate monomer. The term “PMMA”, within the meaning of the invention, denotes homo- and copolymers of methyl methacrylate (MAM), the ratio by weight of MAM in the PMMA preferably being at least 70% by weight for the copolymer from MAM.

The term "copolymer based on methyl methacrylate" means a copolymer having at least one monomer of methyl methacrylate. For example, a copolymer based on methyl methacrylate can be a copolymer comprising at least 70%, preferably 80%, advantageously 90% by weight of MMA in the PMMA.

The term "light molar fraction" means the proportion of a component whose relative volatility, compared to the other components of a mixture, is the highest, the "average molar fraction" the proportion of a component whose the relative volatility, with respect to the other components of the mixture, is average and, “heavy molar fraction”, the proportion of a component whose relative volatility, with respect to the other components of the mixture, is the lowest.

The term “latent heat of vaporization DHn in the standard state”, or even “enthalpy of vaporization”, expressed in J.mol-L, means the enthalpy variation accompanying the vaporization of one mole of a compound.

[0029] The term "molar specific heat in the standard state", expressed in J. mol-1. K-1, the quantity of heat to be supplied to one mole of a compound to raise its temperature by 1°C.

[0030] The term "condensation" means the change of state of a compound passing from a gaseous state to a liquid state. By “vaporization” is meant the change of state of a compound passing from a liquid state to a gaseous state.

Within the meaning of the invention, the term "condensate" means a mixture of compounds obtained at the end of a step of condensing a gas. In the context of the invention, this mixture preferably comprises one or more monomer(s) and an absorbent liquid which has participated, in particular by heat exchange, in the condensation of the monomer(s). The condensate can also correspond to one or more monomer(s) after a purification step. The gas to be condensed comprises at least 30% by weight, preferably at least 40% by weight and more preferably at least 50% by weight of the condensable materials.

[0032] Within the meaning of the invention, the expression “absorbent liquid” corresponds to a compound, in the liquid state at a temperature of 50° C. and a pressure of 1 bar absolute, being capable of absorbing thermal energy coming from of the monomer or monomers of the gaseous effluent.

The term “gaseous effluent” is understood to mean a reaction product resulting from a thermal decomposition and comprising molar fractions which may in particular comprise the monomer(s). The gas to be condensed comprises at least 30% by weight, preferably at least 40% by weight and more preferably at least 50% by weight of the condensable materials.

[0034] By “heat exchange” is meant within the meaning of the invention a system making it possible to transfer heat between a first element and a second element, the first element having a higher temperature than the second element, this causes cooling of the first element and a warm-up of the second. By "bringing into contact" is meant in the sense of the invention a direct contact, that is to say a heat exchange without a separating wall between the first and the second element.

[0035] The expression "fluidic communication" within the meaning of the invention corresponds to the fact that two parts are arranged so as to allow the passage of a fluid from a first part to a second part without there being any leak.

The term "substantially equal" within the meaning of the invention a value varying by less than 30% relative to the compared value, preferably by less than 20%, even more preferably by less than 10%.

In the following description, the same references are used to designate the same elements.

According to one aspect, the invention relates to a method 200 for treating a gaseous effluent. The gaseous effluent generally comes from the pyrolytic decomposition of a polymer or a mixture of polymers. The polymer can for example be polyethylenes such as high density polyethylene (HDPE) or polyethylene tee. rephthalate (PET); polypropylene, polybutadiene and polybutylene, of a homo- and copolymer of olefins such as acrylonitrile-butadiene-styrene copolymers, styrene-butadiene-alkyl methacrylate (or SBM) copolymers; acrylic homo- and copolymers and polyalkyl methacrylates such as poly(methyl methacrylate) (PMMA); a polyhydroxyalkanoate; homo- and copolyamides; polycarbonates; polyesters including poly(ethylene terephthalate) and poly(butylene terephthalate); polyethers such as poly(phenylene ether), poly(oxymethylene), poly(oxyethylene) or poly(ethylene glycol) and poly(oxypropylene); polystyrene; copolymers of styrene and maleic anhydride; poly(vinyl chloride); fluorinated polymers such as poly (vinylidene fluoride), polytetrafluoride of ethylene and polychlorotrifluoro-ethylene; natural or synthetic rubbers; thermoplastic polyurethanes; polyaryl ether ketones (PAEK) such as polyetheretherketone (PEEK) and polyether ketone ketone (PEKK); polyetherimide; polysulfone poly(phenylene sulfide); cellulose acetate; poly(vinyl acetate), polypropiolactone or a mixture of two or more of these polymers.

A PolyHydroxyAlkanoate (PHA) can for example be selected from: poly-3-hydroxybutyrate (P3HB), poly-4-hydroxybutyrate (P4HB), poly-3-hydroxypropionate (P3HP), poly-5- hydroxyvalerate (P5HV), poly-6-hydroxyhexanoate, polylactic acid (PLA), polyglycolic acid, poly-3-hydroxybutyrate-co-3-hydroxypropionate, poly-3-hydroxybutyrate-co-(D) -lactide, poly-3-hydroxybutyrate-co-4-hydroxybutyrate (poly-3HB-co-4HB), poly-3-hydroxybutyrate-co-3-hydroxyvalerate (poly-3-HB-co-3HV), poly-3-hydroxybutyrate-co-5-hydroxyvalerate and poly-3-hydroxybutyrate-co-3-hydroxyhexanoate which are essentially polyesters produced naturally by microorganisms and which are formed by the polymerization of one or more monomers.

Monomer components of PHAs include, but are not limited to, acid or ester forms such as acrylic acid, 3-hydroxybutyric acid, 3-hydroxybutyrate, 3-hydroxypropionate, 3-hydroxyvalerate, 3-hydroxyhexanoate, 3-hydroxyheptanoate, 3-hydroxyoctanoate, 3-hydroxynonanoate, 3-hydroxydecanoate, 3-hydroxydodecanoate, 4-hydroxybutyrate, 4-hydroxyvalerate, 5-hydroxyvalerate, 6-hydroxyhexanoate, 2-Methyl-3-hydroxypropanoate, 2-Methyl-2-hydroxypropanoate, 2-hydroxypropanoate (lactic acid) and 2-hydroxyethanoate (glycolic acid); and/or the lactone or lactam forms such as caprolactone or caprolactam, or propiolactone, butyrolactone, valerolactone. Such monomer components can form

homopolymers or copolymers. Although examples of PHA copolymers having two different monomer components have been provided, the PHA can have more than two different monomer components. During the pyrolysis of PHAs and PLA, other monomeric components can be formed and used as monomers, or as reactants in new syntheses.

[0041] Preferably, the polymer is selected from:

Polymethyl methacrylate (PMMA), a polyhydroxyalkanoate, PLA, polystyrene, copolymers of styrene and anhydride, or a mixture of two or more of these polymers.

[0042] In addition, the polymer may come from a composite material comprising a polymer and a reinforcement.

Such a process makes it possible to recover one or more monomer(s) contained in a gaseous effluent. It is not systematic that the pyrolytic decomposition of a polymer leads to the formation of monomer(s). Thus, it can form during this decomposition of other monomers which are not less advantageous to valorize than a monomer. Thus, the product of interest may be a monomer or a mixture of monomers resulting from the decomposition of the polymer(s). The product of interest can in particular be a monomer or a mixture of monomers resulting from the decomposition of the polymer(s). Typically, at the end of the process, the user will have a fraction enriched in monomers which he can, for example, use as is, further purify or even transform.

The monomer(s) may (wind) for example be selected from the following compounds: methyl methacrylate, methyl acrylate, ethyl acrylate, acrylic acid, methacrylic acid, styrene, crotonic acid, gamma-butyrolactone, delta-valerolactone and mixtures thereof. Preferably, the monomer(s) are selected from the following compounds: methyl methacrylate, methacrylic acid, acrylic acid, styrene, and mixtures thereof.

[0045] Preferably, the gas to be treated comes from the thermal decomposition of a thermoplastic polymer and the product of inter and to be recovered is the monomer of the decomposed polymer. The monomer thus recovered can then be recycled.

For this, the method uses an absorbent liquid which can advantageously be reused in the context of a cyclic condensation system which will be detailed later.

The absorbent liquid is advantageously selected to best promote heat exchange with the gaseous effluent in the condensation chamber 110 on the one hand and partial vaporization of the condensate during expansion in the second chamber 130 on the other hand. . Thus, the choice of absorbent liquid is preferably adapted to the monomer(s) to be recovered. The monomer(s) to be recovered are liquid at atmospheric pressure of 1013 mbar.

Preferably, the absorbent liquid is selected so that the ratio between its latent heat of vaporization DHn in the standard state and its molar specific heat Cp in the standard state is as high as possible and, in all cases , greater than that of the monomer(s) to be recovered. Thus, the effectiveness of the treatment method according to the invention is greatly improved. These values ​​in the standard state of latent heat of vaporization and molar specific heat can be found in the manuals known to those skilled in the art. They preferably correspond to the state at a pressure of 1 bar. The latent heat of vaporization DHn in the standard state of the absorbent liquid is for example greater than or equal to 20 kJ/mole, preferably greater than or equal to 30 kJ/mole, more preferably greater than or equal to 40 kJ/mole, and even more preferably greater than or equal to 50 kJ/mole.

Advantageously, the absorbent liquid is chosen from one of the following compounds: benzene, benzonitrile, a compound of formula R-OH, a compound of formula R-COOH, in which R can be chosen from alkyls, whose number of carbons is between 1 and 5, a phenyl or a hydrogen. Thus, the absorbent liquid can for example be selected from: benzene (71-43-2), benzonitrile (100-47-0), dihidrogen monoxide (7732-18-5), methanol (67-56 -1), ethanol (64-17-5), propanol (71-23-8 or 67-63-0), butanol (71-36-3; 78-92-2; 15892-23-6 14898-79-4; 4221-99-2), phenol (108-95-2), formic acid (64-18-6), acetic acid (64-19-7) or mixtures thereof .

In a first mode more advantageously, for environmental and ecological reasons, the absorbent liquid is chosen from one of the following compounds: a compound of formula R-OH, a compound of formula R-COOH, in which R can be chosen from alkyls, the number of carbons of which is between 1 and 5, or a hydrogen. Thus, the absorbent liquid can for example be selected from: dihidrogen monoxide (7732-18-5), methanol (67-56-1), ethanol (64-17-5), propanol (71- 23-8 or 67-63-0), butanol (71-36-3; 78-92-2; 15892-23-6; 14898-79-4; 4221-99-2), formic acid (64 -18-6), acetic acid (64-19-7) or mixtures thereof.