Depolymerization method and system

Abstract

Depolymerization method and system. A depolymerization method for recovering monomers from a polymer is provided, the method comprising the sequential steps of pyrolyzing a polymer-containing feedstock in a pyrolysis reactor to produce a gas stream, directing the gas stream from the pyrolysis reactor to a separator configured to remove impurities from the gas stream, and directing the gas stream from the separator to a condenser for condensing monomers contained in the gas stream. The temperature of the gas stream in the separator is maintained at or above the boiling point of the monomers.

Description

[Technical field]

[0001] The project leading to this application has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement no. 820687.

[0002] The present invention relates to the field of depolymerization for the recovery of monomers from feeds containing polymers of which they are constituents.

[0003] The present invention more particularly relates to a thermal depolymerization process that includes pyrolysis of a feedstock, i.e., heating the feedstock in the substantial absence of oxygen, for example to at least partially vaporize the feedstock. Pyrolysis of the feedstock produces a gas stream that includes monomer vapor. [Background technology]

[0004] A problem that arises in such depolymerization methods is that in addition to vaporized monomer, the gas stream produced by pyrolysis may contain impurities such as dust, mist droplets, residual polymer chains, oligomers and / or contaminants.

[0005] Such impurities may modify components of the depolymerization system located downstream of the pyrolysis reactor and thus adversely affect productivity, or may contaminate the monomers obtained from the vaporized monomer, e.g., removed as crude monomer or oil monomer.

[0006] JP3210323 and DE3146194 each disclose a depolymerization process for recovering monomers from a polymer, the depolymerization process comprising pyrolyzing a polymer-containing feedstock in a pyrolysis reactor to produce a gas stream containing, for example, monomer vapor, and passing the gas stream through a separator to, for example, remove impurities from the gas stream.

[0007] WO2016 / 030460 discloses a depolymerization process for recovering monomers from a polymer, comprising pyrolyzing a polymer-containing feedstock in a pyrolysis reactor to produce a gas stream containing, for example, monomer vapor, and passing the gas stream through a contactor comprising a perforated plate arranged to flow long chain components back into the pyrolysis reactor.

[0008] US10731080 discloses a depolymerization process for recovering monomers from a polymer, comprising pyrolyzing a waste material containing a polymer to produce a gas stream, quenching the gas stream output from the pyrolysis reactor in a quenching device for removing oligomers from the gas stream, and sending the oligomers back to the pyrolysis reactor.

[0009] WO2014 / 040634 discloses a method and an apparatus for recycling waste plastics. The method includes pyrolysis of waste plastics in the presence of a catalyst and an adsorbent in a pyrolysis reactor at a temperature comprised between 350 and 500° C., separation in a gas-solid separation system comprising a separator and a cyclone, purification of the gas in an electric separator, and cooling of the gas in a condenser to obtain a purified liquid product in a conduit. The remaining gas stream is sent to a regeneration device via a conduit. The gas is sent back to the extruder that feeds the pyrolysis reactor, and the heavier particles are transported to the pyrolysis reactor again.

[0010] EP3031881 discloses a method for pyrolytic processing of waste polymers from recycling food packaging, and a system for carrying out such a method. The method comprises pyrolysis of waste plastics in a thermal reactor, separation in a collection chamber, separation in a cyclone, separation in an oil scrubber, and condensation. The temperature at the outlet of the thermal reactor is comprised between 600°C and 800°C.

[0011] US10301235 discloses a system and method for recycling waste plastics, more specifically a method for depolymerizing polystyrene, which includes the steps of pyrolyzing the feed in a pyrolysis reactor, quenching the pyrolysis gas in a quenching device and condensing the oligomers, which are sent back to the pyrolysis reactor, and the gas stream is discharged to a condenser to condense the styrene to obtain styrene oil. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] JP3210323 [Patent Document 2] DE3146194 [Patent Document 3] WO2016 / 030460 [Patent Document 4] US10731080 [Patent Document 5] WO2014 / 040634 [Patent Document 6] EP3031881 [Patent Document 7] US10301235 Summary of the Invention [Problem to be solved by the invention]

[0013] One of the aims of the present invention is to propose a depolymerization process capable of producing monomers, in particular crude monomers or pyrolysis oils, with a satisfactory quality and with a satisfactory productivity. [Means for solving the problem]

[0014] To that end, the present invention relates to a depolymerization process for recovering monomers from a polymer, the process comprising the steps of: - pyrolyzing a polymer-containing feedstock in a pyrolysis reactor to produce a gas stream; - directing the gas stream from the pyrolysis reactor to a separator configured to remove impurities from the gas stream; - directing the gas stream from the separator to a condenser for condensing monomers contained in the gas stream. wherein the temperature of the gas stream in the separator is maintained above the boiling point of the monomer.

[0015] By maintaining the temperature of the gas stream in the separator above the boiling point of the monomer, any monomer that condenses in the separator can be vaporized, or most of the monomer can be vaporized.

[0016] Preferably, the temperature should be low enough to promote condensation in the separator of any dimers or trimers that are present in the gas stream or that may form again from monomers in the separator.

[0017] In a specific embodiment, it may also be possible to capture mist droplets in the separator for improved efficiency without clogging the separator, making it possible to collect mist droplets that are generated around fine dust particles carried in the gas stream entering the separator.

[0018] According to certain embodiments, the depolymerization method comprises one or more of the following optional features, individually or in any technically feasible combination: - the temperature of the gas stream in the separator is below the boiling point of the dimers of the monomer and / or below the boiling point of the trimers of the monomer, at least in the downstream section of the separator; - the maximum cross-sectional area of ​​the internal flow passage of the separator is at least 0.001 times the mass flow rate of the gas stream entering the separator during operation, and the area is expressed in square meters (m 2 ) and mass flow rate is expressed in kilograms per hour (kg / hr), - the area of ​​the largest cross-section of the internal flow passages in the separator is at least 10 times the area of ​​the smallest cross-section in the separator; - the linear velocity of the gas stream in the separator is less than the maximum linear velocity; the maximum linear velocity is 0.50 m / s, in particular 0.15 m / s, more in particular 0.10 m / s; the area of ​​the maximum cross section of the internal flow passages of the separator is selected as a function of the maximum feed rate of the pyrolysis reactor, the depolymerization temperature of the polymer and the molar mass of the polymer, such that the linear velocity of the gas stream in the downstream section of the inlet duct is lower than the maximum linear velocity at the maximum feed rate of the pyrolysis reactor, the residence time of the gas stream in the separator is comprised between 1 and 30 seconds, preferably between 5 and 25 seconds, and more preferably between 10 and 20 seconds; - the method includes the step of atomizing liquid monomer removed from a condenser in a separator, the liquid monomer being sprayed into the gas stream; - the low-temperature monomer is sprayed into the separator such that the mass flow rate of the low-temperature monomer sprayed into the separator is not more than 93%, more preferably not more than 83%, more preferably not more than 73%, more preferably not more than 63%, more preferably not more than 53% of the overall mass flow rate of the compounds fed to the separator, - liquid monomer is sprayed into the separator in such a way that the mass flow rate of the cold monomer sprayed into the separator is at least 10%, more preferably at least 20%, preferably at least 30%, more preferably at least 40%, more preferably at least 50% of the overall mass flow rate of the compounds fed to the separator, - the gas stream slows down gradually in the separator, - the cross section of the internal flow passage of the separator gradually increases when taking into account the flow direction of the gas stream; - the separator comprises a separation chamber extending along a central axis, the separator being configured such that the gas stream flows circulatingly through the separation chamber; - the separator has an inlet duct for receiving the gas stream produced by the pyrolysis reactor, the inlet duct opening into the separation chamber; - the inlet duct extends around the separation chamber; - the method comprises the step of coalescing mist droplets present in the gas stream by providing an internal mist removal device within the separator.

[0019] The present invention also provides a depolymerization system configured to carry out the above-described depolymerization method for recovering monomers from a polymer, comprising: - a pyrolysis reactor for pyrolyzing a polymer-containing feedstock to produce a gas stream from the feedstock; - a separator for receiving the gas stream from the pyrolysis reactor and for removing impurities from the gas stream; a condenser for receiving the gas stream from the separator for condensing monomers contained in the gas stream; and configured such that during operation, the temperature of the gas stream in the separator is maintained at or above the boiling point of the monomer.

[0020] The invention and its advantages will be better understood on reading the following description, given by way of non-limiting example only, and on referring to the accompanying drawings, in which: [Brief description of the drawings]

[0021] [Figure 1] FIG. 1 is a schematic diagram illustrating a depolymerization system for carrying out a depolymerization method for recovering monomers from a feed containing a polymer of which the monomers are constituents. [Diagram 2] FIG. 2 is a schematic side view of a separator that can be used in the depolymerization system of FIG. [Diagram 3] FIG. 3 is a schematic top view of the alternative separator of FIG. 2. [Figure 4] FIG. 4 is a schematic exploded side view of the separator of FIG. 3. [Diagram 5] FIG. 2 is a schematic side view of a separator. [Figure 6] FIG. 2 is a schematic side view of a separator. [Figure 7] FIG. 2 is a schematic top view of a separator with an inlet collector. [Figure 8] FIG. 2 is a schematic side view of an inlet collector. [Figure 9] FIG. 2 is a schematic exploded view of the separator. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] The depolymerization system 10 illustrated in FIG. 1 is configured to perform a depolymerization process for recovering monomers from a feed material containing polymers of which the monomers are constituents.

[0023] The depolymerization method includes the successive steps of pyrolyzing a feedstock containing a polymer in a pyrolysis reactor 12 configured to produce a gas stream from the feedstock, the gas stream containing monomers that are constituents of the polymer, the monomers being in a gaseous state, directing the gas stream from the pyrolysis reactor 12 to a separator 14 configured to remove impurities from the gas stream, and directing the gas stream from the separator 14 to a condenser 16 configured to condense the gaseous monomers contained in the gas stream to monomers in a liquid state.

[0024] During the depolymerization process, the pyrolysis is operated such that the gas stream provided to separator 14 contains monomer in a gaseous state, hereinafter also referred to as "gaseous monomer."

[0025] During the depolymerization process, the condensate provided by the condenser 16 contains monomer in a liquid state, hereinafter also referred to as "liquid monomer" or "low temperature monomer", or pyrolysis oil.

[0026] The depolymerization system 10 comprises a pyrolysis reactor 12, a separator 14, and a condenser 16, fluidly connected in series, in that order.

[0027] As described in more detail below, other components of the depolymerization system 10 may optionally be incorporated between the pyrolysis reactor 12 and the separator 14, or between the separator 14 and the condenser 16, or downstream of the condenser 16.

[0028] Pyrolysis reactor 12 includes a reactor inlet 12A for receiving a feedstock and a reactor outlet 12B for providing a gas stream resulting from the pyrolysis of the feedstock.

[0029] Pyrolysis reactor 12 is configured to heat a feedstock received at reactor inlet 12A to an elevated temperature, for example to vaporize the feedstock and produce a gas stream provided at reactor outlet 12B.

[0030] Optionally, the pyrolysis reactor 12 is configured to mechanically process the feed material. Mechanical processing of the feed material in addition to heating the feed material facilitates the production of a gas stream.

[0031] Mechanical processing of the feed material in pyrolysis reactor 12 can include, for example, stirring and / or pushing the feed material. Thus, pyrolysis reactor 12 can be configured, for example, to stir the feed material and / or to push the feed material.

[0032] The pyrolysis reactor 12 is configured, for example, as a heated screw extruder, in particular a heated twin-screw extruder.

[0033] A heated screw extruder comprises a tubular barrel, at least one screw extending into the barrel and rotatably driven to extrude a feed material along the tubular chamber, and a heating system for heating the feed material contained within the barrel. A heated twin-screw extruder is a heated screw extruder comprising two screws extending side-by-side into the barrel, the threads of the screws preferably intermeshing, and the screws co-rotating (rotating in the same direction about their respective axes) or counter-rotating (rotating in opposite directions about their respective axes).

[0034] Separator 14 includes a separator gas inlet 14A for receiving the gas stream produced by pyrolysis reactor 12 and a separator gas outlet 14B for providing a gas stream that is directed to condenser 16.

[0035] The separator 14 has an internal flow path for the gas stream from a separator gas inlet 14A to a separator gas outlet 14B. The internal flow path has an upstream section adjacent the separator gas inlet 14A and a downstream section adjacent the separator gas outlet 14B.

[0036] The internal flow passage has a cross section taken substantially perpendicular to the flow of gas within the internal flow passage. The cross section has an area (i.e., a measure of the extent of the cross section).

[0037] The cross-sectional area of ​​the internal flow passage of separator 14 may be constant along the internal flow passage, or may vary along the internal flow passage.

[0038] Hereinafter, the "largest cross-section" of the internal flow passage of separator 14 refers to the section of the internal flow passage of separator 14 having the cross-section with the largest area.

[0039] Optionally, separator 14 includes an impurity outlet 14C for collecting impurities separated from the gas stream in separator 14.

[0040] The separator of the present invention is not a standard cyclone, by which is understood a device having a gas inlet velocity in the range of 30 m / s to 45 m / s.

[0041] Condenser 16 includes a condenser inlet 16A for receiving the gas stream provided by separator 14 and a condenser outlet 16B for providing a condensate, i.e., a product condensed within condenser 16.

[0042] Condenser 16 is configured to condense a gas stream received at condenser inlet 16A to provide a condensate at condenser outlet 16B.

[0043] Condenser 16 optionally includes a gas outlet 16C for providing non-condensable products that pass through condenser 16 without condensing.

[0044] The depolymerization process is carried out such that the gas stream in separator 14 is at a temperature above the boiling point of the monomer.

[0045] The gas stream produced by pyrolysis gradually cools as it travels along the internal flow path of the separator 14. The temperature of the gas stream within the separator 14 is lowest in the downstream section of the separator 14.

[0046] Thus, in other words, the depolymerization process is carried out such that the temperature of the gas stream in the downstream section of separator 14 is at or above the boiling point of the monomer.

[0047] This promotes evaporation of any liquid monomer present in the gas stream into gaseous monomer, which prevents polymerization of the monomer.

[0048] The gas stream may contain dimers or trimers, i.e., chains of two monomers or chains of three monomers, which may result from incomplete depolymerization or polymerization of the monomers during pyrolysis.

[0049] Generally, the boiling points of the dimers and trimers of a monomer are strictly higher than the boiling point of the monomer.

[0050] Preferably, the depolymerization process is carried out such that the temperature of the gas stream in the downstream section of separator 14 is at a temperature that is strictly below the boiling point of the dimer of the monomer and / or is strictly below the boiling point of the trimer of the monomer.

[0051] This causes most of the dimers and / or trimers present in the gas stream to condense within separator 14 , thus retaining the dimers and trimers within separator 14 and limiting or preventing them from flowing to condenser 16 .

[0052] The depolymerization process is for example carried out with polymethyl methacrylate (PMMA), which refers to a homopolymer or copolymer of methyl methacrylate (MMA) containing at least 50% by weight, preferably at least 60% by weight, more preferably at least 70% by weight, advantageously at least 80% by weight, and even more advantageously at least 90% by weight of methyl methacrylate.

[0053] In the case of PMMA (polymer) and MMA (monomer), the boiling point of MMA is about 100° C., while the boiling points of the dimer and trimer are about 200° C. and 300° C., respectively.

[0054] In such a case, the depolymerization process is therefore carried out such that the temperature of the gas stream in the downstream section of the separator 14 is comprised between 100°C and 280°C, in particular between 140°C and 180°C.

[0055] During the performance of the depolymerization process, the absolute pressure of the gas stream in separator 14 is preferably comprised between 0.35 bar and 5 bar, preferably between 0.5 bar and 4 bar, more preferably between 1 bar and 3 bar.

[0056] Advantageously, the depolymerization process comprises the step of spraying the liquid monomer withdrawn from the condenser 16 into the separator 14, the liquid monomer being sprayed into, and preferably against, the gas stream.

[0057] Optionally, the depolymerization method includes spraying a fraction of the liquid monomer recovered by condenser 16 into separator 14.

[0058] In such a case, the depolymerization system 10 is configured to spray a fraction of the liquid monomer recovered by the condenser 16 into the separator 14 .

[0059] The depolymerization process of the present invention does not include the step of reinjecting or refeeding any liquid components or any solid components coming from the pyrolysis reactor towards the pyrolysis reactor.

[0060] The depolymerization system 10 includes a monomer return line 18 configured, for example, to collect the liquid monomer provided by the condenser 16 and spray the liquid monomer into the separator 14 .

[0061] Optionally, the depolymerization method includes a step of reinjecting liquid monomer collected at liquid outlet 16B of condenser 16 into gas entering inlet 16A of condenser 16 from the outlet of condenser 16 toward the inlet of condenser 16.

[0062] This reduces the temperature of the gas entering the condenser 16 and increases the efficiency of the condenser 16 .

[0063] In such a case, the depolymerization system 10 includes a reinjection line 19 configured to collect the liquid monomer at the liquid outlet 16B of the condenser 16 and reinject the liquid monomer into the gas inlet 16A of the condenser 16.

[0064] Optionally, the depolymerization method includes purifying the condensate provided by condenser 16 to remove solid particles from the condensate provided by condenser 16.

[0065] In such a case, the depolymerization system 10 includes a purification device 20 configured to remove solid particles from the condensate provided by the condenser 16 .

[0066] The liquid monomer sprayed into separator 14 may be purified liquid monomer that has been purified to remove solid particles before being sprayed into separator 14, or untreated liquid monomer as provided by condenser 16 may be sprayed directly into the separator.

[0067] Correspondingly, in the depolymerization system 10, the monomer return line 18 is supplied with purified condensate provided by a purification device 20 as illustrated in FIG. 1, or alternatively, the monomer return line 18 is supplied with raw condensate provided directly by the condenser 16.

[0068] Preferably, the liquid monomer is sprayed into separator 14 such that the ratio of the mass flow rate of the liquid monomer sprayed into separator 14 to the mass flow rate of the gas stream is 93% or less, more preferably 83% or less, more preferably 73% or less, more preferably 63% or less, and more preferably 53% or less.

[0069] Preferably, the liquid monomer is sprayed into separator 14 such that the mass flow rate of the liquid monomer sprayed into separator 14 relative to the mass flow rate of the gas stream is 10% or more, more preferably 20% or more, preferably 30% or more, more preferably 40% or more, and more preferably 50% or more.

[0070] Optionally, instead of or in addition to spraying liquid monomer, the depolymerization method includes spraying liquid water into separator 14. The advantages are similar to those of spraying liquid monomer into separator 14.

[0071] Optionally, the liquid monomer reinjected into the condenser gas inlet 16A may be purified liquid monomer that has been purified to remove solid particles prior to reinjection into the condenser 16, or may be as provided by the condenser 16 directly.

[0072] Correspondingly, in the depolymerization system 10, the reinjection line 19 is supplied with purified condensate provided by a purification device 20 as illustrated in FIG. 1, or alternatively, the reinjection line 19 is supplied with raw condensate provided directly by the condenser 16.

[0073] The depolymerization system of the present invention does not include reinjection lines or the like for either liquids or solids directed to the pyrolysis reactor.

[0074] The pyrolysis reactor 12 is configured to process the feedstock at a maximum mass flow rate and thus provide a gas stream at a maximum mass flow rate.

[0075] Furthermore, at any section of the internal flow path of separator 14, the gas stream flowing within separator 14 has a linear velocity determined as the volume of gas produced by pyrolysis reactor 12 per unit of time divided by the cross-sectional area of ​​said section of the internal flow path of separator 14.

[0076] Preferably, the depolymerization process is carried out such that the linear velocity of the gas stream within separator 14 is less than the maximum linear velocity, at least in the section of the internal flow path of separator 14 having the largest cross section.

[0077] In certain embodiments, the section of the internal flow path of separator 14 having the largest cross section is the downstream section of the internal flow path of separator 14 .

[0078] In one embodiment, particularly when the polymer is PMMA, the maximum linear velocity is 0.50 m / s, preferably 0.15 m / s, especially 0.10 m / s.

[0079] The linear velocity of the gas stream in any section of the internal flow path of the separator 14 is a function of the mass flow rate of the gas stream or the volumetric flow rate of the gas stream and the cross-sectional area of ​​said section of the internal flow path of the separator 14. The mass flow rate is related to the volumetric flow rate and mass density of the gas stream at the operating pressure.

[0080] The volumetric flow rate of the gas stream is a function of the feed rate of the pyrolysis reactor 12, the depolymerization temperature of the polymer, and the molar mass of the polymer.

[0081] Advantageously, the area of ​​the maximum cross section of the internal flow passages of the separator 14 is selected as a function of the maximum feed rate of the pyrolysis reactor 12, the depolymerization temperature of the polymer and the molar mass of the polymer, for example, so that the linear velocity of the gas stream at the maximum cross section of the internal flow passages of the separator 14 is lower than the maximum linear velocity at the maximum feed rate of the pyrolysis reactor.

[0082] Preferably, the maximum cross-sectional area of ​​the internal flow passage of the separator 14 has an area in square meters (m2) that is at least 0.001 times the maximum mass flow rate of the gas stream provided by the pyrolysis reactor 12. 2 ) and the maximum mass flow rate is expressed in kilograms per hour (kg / hr).

[0083] Preferably, the maximum cross-sectional area of ​​the internal flow passages of separator 14 is at least 10 times the minimum cross-sectional area of ​​separator 14 .

[0084] These parameters make it possible to limit the linear velocity of the gas stream in the separator 14 and therefore favour the deposition of dust and liquid droplets carried by the gas stream and thus their separation from the gas stream. Indeed, the lower the linear velocity of the gas stream, the less liquid droplets and dust are carried by the gas stream.

[0085] Advantageously, the depolymerization process includes gradually slowing the gas stream in separator 14 .

[0086] This can be achieved, for example, by gradually increasing the cross section of the internal flow passage of the separator 14 from the separator gas inlet 14A to the separator gas outlet 14B.

[0087] In such a case, the downstream section of the internal flow path of the separator 14 is the section of the internal flow path of the separator 14 having the largest cross-section.

[0088] Advantageously, the residence time of the gas stream in the separator 14 is comprised between 1 and 30 seconds, preferably between 5 and 25 seconds, and even better between 10 and 20 seconds.

[0089] Residence time is the time required for a gas stream to flow from the separator inlet 14A to the separator outlet 14B.

[0090] The residence time is a function of the length of the internal flow path of separator 14 , the average temperature, the mass flow rate or volumetric flow rate and molecular weight, and the volume of separator 14 .

[0091] The gas stream produced by the pyrolysis reactor 12 may contain mist formed of mist droplets. The mist droplets may form around dust particles present in the gas stream. The dust particles may result from impurities in the feed material containing the polymer intended to be depolymerized. The mist droplets present in the gas stream may include liquid monomer, liquid dimer or liquid trimer carried on dust particles present in the gas stream.

[0092] Advantageously, the depolymerization method includes the step of de-misting the gas stream (e.g., by passing the gas stream through a mist eliminator or mist removal device) and / or the step of sublimating the gas stream (i.e., by passing the gas stream through a sublimator or sublimation device).

[0093] Mist removal is distinct from condensing the gaseous monomer into the liquid monomer, and consists of collecting the liquid droplets already present in the gas stream, e.g., droplets in a mist.

[0094] Mist removal is achieved, for example, by favoring coalescence of mist droplets present in the gas stream, for example by defining micropassages that cause the droplets to flow closer together and then coalesce.

[0095] Mist removal is achieved, for example, by providing at least one mist removal device, each mist removal device configured to favour coalescence of mist droplets such that they become too heavy to be carried by the gas stream.

[0096] Each mist removal device may comprise a cyclone effect chamber, at least one grid, at least one mesh, at least one piece of foam, at least one porous monolith, and / or at least one baffle for trapping mist droplets, for example by favouring coalescence of the mist droplets.

[0097] Mist removal may occur, for example, within the separator 14, between the separator 14 and the condenser 16, or downstream of the condenser 16.

[0098] Optionally, the depolymerization method includes de-misting the gas stream in separator 14.

[0099] In such a case, the separator 14 includes an internal mist elimination device located within the separator 14 .

[0100] Optionally, the depolymerization method includes de-misting the gas stream downstream of separator 14 and upstream of condenser 16, i.e., between separator 14 and condenser 16.

[0101] In such a case, the depolymerization system 10 includes an upstream mist removal device 22 disposed in series between the separator 14 and the condenser 16, the upstream mist removal device 22 configured to capture mist droplets present in the gas stream.

[0102] An upstream mist removal device 22 is positioned downstream of the pyrolysis reactor 12 and upstream of the separator 14 .

[0103] Optionally, the depolymerization method includes a step of de-misting the gas stream downstream of the condenser 16.

[0104] In such a case, the depolymerization system 10 includes a downstream mist removal device 24 disposed downstream of the condenser 16, the downstream mist removal device 24 configured to remove liquid droplets present in the gas stream.

[0105] Condensation differs from mist removal because it provides for the retention of the gaseous portion of the gas stream as a solid.

[0106] Sublimation involves passing the gas stream through a chamber containing cooled thin plates or fins such that the product, which is separated from the remainder of the gas stream, sublimes near or below the triple point and adheres to the thin plates or fins in crystalline form.

[0107] In the sublimator, the separated product gradually accumulates in crystalline form and can be drained by heating the crystallized separated product so that it melts. It is necessary that the separated product to be captured can be heated so that it melts without polymerizing.

[0108] In the case of depolymerization of PMMA, it may be appropriate to provide a sublimator to remove terephthalic acid of dimethyl terephthalate that may be present in the gas stream, produced by PET contamination.

[0109] Providing a sublimator may be appropriate, for example, when there is a risk of contamination with polyolefins such as PE, which have a high melting point and can produce wax that can become trapped in the condenser 16 .

[0110] The sublimation unit may comprise two sublimators fluidly connected in parallel such that one of the two sublimators can be maintained in operation while the other is drained, thus allowing continuous operation of the depolymerization system 10.

[0111] Optionally, the depolymerization method includes passing the gas stream through a condenser to capture contaminants present in the gas stream.

[0112] If a sublimator is provided, it is preferably located between the separator 14 and the condenser 16 .

[0113] As illustrated in FIG. 1, the depolymerization system 10 includes at least one sublimator 25, each sublimator 25 provided between the separator 14 and the condenser 16 to treat a gas stream flowing from the separator 14 to the condenser 16.

[0114] The depolymerization system 10 may, for example, include two sublimators 25 provided in parallel with each other between the separator 14 and the condenser 16, each of which may process a gas stream while the other is being discharged.

[0115] Optionally, the depolymerization method includes the step of discharging the non-condensed products provided by condenser 16.

[0116] In such a case, the depolymerization system 10 includes a discharge device 26 for discharging the non-condensed products. The discharge device 26 is positioned to receive the gas stream provided by the condenser 16 at the gas outlet 16B of the condenser 16.

[0117] If a downstream mist elimination device 24 is provided, it is preferably arranged in series between the condenser 16 and the exhaust device 26 .

[0118] A separator 14 suitable for use in the depolymerization system 10 to carry out the depolymerization method is illustrated in FIG.

[0119] The separator 14 includes an internal flow passage 30 configured for circulation of a gas stream between a separator inlet 14A and a separator outlet 14B.

[0120] In one example, as illustrated in FIG. 2, the pyrolysis reactor outlet 12B opens directly into the separator inlet 14A such that the gas stream produced by the pyrolysis reactor 12 flows directly from the pyrolysis reactor outlet 12B.

[0121] Preferably, when the pyrolysis reactor 12 has at least one extrusion screw, the extrusion screw is inserted or protrudes into the separator inlet 14A to avoid blockage of the reactor outlet 12B by impurities.

[0122] In other words, the pyrolysis reactor outlet 12B is directly fluidly connected to the separator inlet 14A such that the gas stream produced by the pyrolysis reactor 12 flows directly from the pyrolysis reactor outlet 12B, which is directly connected to the separator inlet 14A, without passing through any other fluid conducting elements.

[0123] The separator 14 includes, for example, a separation chamber 32 extending about a central axis A, and the separator 14 is configured such that the gas stream flows circulatoryly within the separation chamber 32 about the central axis A.

[0124] Thus, the separator 14 is configured to provide a cyclone effect within the separation chamber 32 .

[0125] In such a configuration, the gas stream flows faster at the periphery of the separation chamber 32 and slower in the center of the separation chamber 32, and impurities present in the gas stream tend to remain at the periphery of the separation chamber 32.

[0126] The separator 14 includes an inlet duct 34 configured to receive the gas stream produced by, for example, the pyrolysis reactor 12. The inlet duct 34 extends from a separator inlet 14A that defines an upstream end of the inlet duct 34. The inlet duct 34 forms an upstream section of the interior volume 30 of the separator 14.

[0127] In consideration of promoting circulatory flow of the gas stream within the separation chamber 32, for example, the inlet duct 34 exits into the separation chamber 32 so as to impart a rotational movement about the central axis A to the gas stream within the separation chamber 32, for example.

[0128] In certain embodiments, the inlet duct 34 opens into the separation chamber 32 such that the gas stream exits into the separation chamber 32 along an inlet direction that defines a non-zero angle with respect to a radial direction that is radial to the central axis A.

[0129] In a variant in which the separator 14 does not have an inlet duct 34, for example, the separator inlet 14A opens into the separation chamber 32, for example to impart a rotational motion about the central axis A to the gas stream in the separation chamber 32.

[0130] In certain embodiments, the separator inlet 14A opens into the separation chamber 32 such that the gas stream exits the separation chamber 32 along an inlet direction that defines a non-zero angle with respect to a radial direction that is radial to the central axis A, for example.

[0131] Advantageously, the inlet duct 34 extends about a central axis A. This makes it possible to obtain a cyclone or rotation effect within the inlet duct 34.

[0132] The separator 14 is preferably configured to collect the gas stream in the center of the separation chamber 32 and provide the gas stream collected in the center of the separation chamber 32 to a separator outlet 14B.

[0133] The separator 14, for example, comprises a collection tube 36 located centrally in the separation chamber 32, the collection tube 36 extending along a central axis A and having at least one inlet opening 38 for the gas stream present in the separation chamber 32 to enter the collection tube 36, and the collection tube 36 is fluidly connected to the separator outlet 14B to provide the collected gas stream to the separator outlet 14B.

[0134] The collection tube 36 for example comprises at least one inlet section 40 , each inlet section 40 comprising one inlet opening 38 or several inlet openings 38 distributed around the circumference of the inlet section 40 of the collection tube 36 .

[0135] The collection tube 36 may, for example, have a number of inlet sections 40 distributed along the collection tube 36, with each inlet section 40 having one inlet opening 38 or several inlet openings 38 distributed around the circumference of the inlet section 40 of the collection tube 36.

[0136] In a preferred embodiment, the collection tube 36 is provided with at least one frusto-conical baffle 42, each having a smaller diameter upper end connected to the collection tube 36 and a free larger diameter lower end, the baffles 42 extending around the respective inlet sections 40.

[0137] Preferably, each inlet section 40 is associated with a respective frusto-conical baffle 42 that extends around the inlet section 40 .

[0138] Preferably, the upper end of each frusto-conical baffle 42 is located above each inlet opening 38 of the corresponding inlet section 40 and the lower end of said frusto-conical baffle 42 is located below each inlet opening 38 of the corresponding inlet section 40.

[0139] Each frusto-conical baffle 42 causes the gas stream to flow beneath the lower end of the frusto-conical baffle 42 before entering the inlet opening 38 of the corresponding inlet section 40 .

[0140] Each frusto-conical baffle 42 favors impurities falling to the bottom of the separation chamber 32 and / or accumulating on the frusto-conical baffle 42 .

[0141] Preferably, each inlet opening 38 has a diameter of 3 to 79 mm. 2 Between 12 and 51 mm, preferably 2 The area is between .

[0142] Preferably, each inlet opening 38 has a circular contour with a diameter comprised between 2 and 10 mm, preferably between 4 and 8 mm.

[0143] Preferably, the cumulative area of ​​the inlet openings 38 (ie the sum of the areas of all the inlet openings 38 ) is comprised between 0.01 and 0.1 times the area of ​​the cross-section of the upstream section of the internal flow passage 30 of the separator 14 .

[0144] In the separator 14 of FIG. 2, the upstream section of the internal flow passage 30 of the separator 14 corresponds to the upstream end of the inlet duct 34 .

[0145] Advantageously, the separator 14 is configured such that the largest cross-section of the separator 14 is located in the downstream section of the separator 14 .

[0146] In the separator 14 illustrated in FIG. 2, the downstream section of the separator 14 is defined by a separation chamber 32 .

[0147] In one example in which the separator 14 comprises an inlet duct 34 and a separation chamber 32, the inlet duct 34 has a cross-section that gradually increases from its upstream end, which receives the gas stream, to its downstream end, which opens into the separation chamber 32.

[0148] Thus, the gas stream gradually slows in the inlet duct 34 until the gas stream reaches the separation chamber 32 .

[0149] For example, the inlet duct 34 may have a height that gradually increases in the downstream direction and / or a width that gradually increases along the inlet duct 34 in the downstream direction, e.g., to increase the cross-sectional area of ​​the inlet duct 34 in the downstream direction.

[0150] Advantageously, as illustrated in Figure 2, the separator 14 is configured to spray the liquid monomer into the gas stream within the separator 14. The separator 14 is configured to spray one or more spray jets into the gas stream within the separator 14.

[0151] To this end, the separator 14 is equipped with at least one spray nozzle 44 for spraying the liquid monomer in the separator 14. Each spray nozzle 44 is configured to spray a spray jet.

[0152] The direction of each atomizing jet may be parallel, perpendicular or oblique to the gas flow, hi one example, each atomizing jet faces the gas flow, i.e., sprays upstream into the gas stream.

[0153] Each spray nozzle 44 is fluidly connected to the condenser 16 and, more specifically, to the return line 18 .

[0154] Each spray nozzle 44 is positioned, for example, to spray liquid monomer into separation chamber 32 .

[0155] As illustrated in FIG. 2, the separator 14 is equipped with a spray nozzle 44, for example, positioned to spray liquid monomer, here upstream in the gas stream, at the inlet of the separation chamber 32, i.e., at the point where the inlet duct 34 connects to the separation chamber 32.

[0156] Advantageously, the separator 14 integrates an internal mist removal device 46 located within the separator 14 for the deposition of mist droplets carried by the gas stream.

[0157] The internal mist removal device 46 comprises, for example, at least one grid 48 extending across a cross section of the separator 14 such that the gas stream flows through openings in the grid 48 .

[0158] In one example where the separator 14 includes an inlet duct 34 , each grid 48 is located, for example, inside the inlet duct 34 .

[0159] 2, the separator 14 includes two grids 48 disposed within the inlet duct 34. The two grids 48 are spaced apart from each other along the inlet duct 34.

[0160] The inlet duct 34 is defined between a lower surface 50 and an upper surface 52 .

[0161] In one example, the lower duct surface 50 is sloped and / or the upper duct surface 52 is sloped.

[0162] In particular, the lower duct surface 50 is sloped and / or the upper duct surface 52 is sloped such that the cross section of the inlet duct 34 increases from the upstream end of the inlet duct 34 towards the downstream end of the inlet duct 34 .

[0163] 2, the duct undersurface 50 slopes downward from the upstream end of the inlet duct 34 to the downstream end of the inlet duct 34. Mist droplets that accumulate on the duct undersurface 50 tend to flow by gravity toward the separation chamber.

[0164] In one example, the inlet duct 34 extends around the separation chamber 32 at least partially around the periphery of the separation chamber 32 .

[0165] As illustrated in FIG. 3, the inlet duct 34 extends around the separation chamber 32 approximately 270° around the central axis A.

[0166] During operation, the gas stream is hot when it enters the separator 14, and the temperature of the gas stream tends to become lower as it travels through the separator 14 due to heat losses, even if the separator 14 is properly insulated. If liquid monomer spray into the separator 14 is provided, this spray tends to further cool the gas stream within the separator 14 due to vaporization of the liquid monomer sprayed into the hot gas stream.

[0167] An inlet duct 34 , which partially surrounds the separation chamber 32 , is beneficial for maintaining the gas stream at a sufficiently high temperature within the separator 14 , and particularly within the separation chamber 32 .

[0168] As illustrated in FIG. 4, in one exemplary embodiment, separator 14 includes a lower portion 60 and an upper portion 62 that mates with lower portion 60 to form separator 14 .

[0169] The lower portion 60 includes a bottom 64 and a peripheral wall 66 extending upwardly from a periphery of the bottom 64, the peripheral wall 66 defining an upper opening 68 and an interior volume 70. The peripheral wall 66 includes a side opening that defines the inlet opening 14A of the separator 14. The peripheral wall 66 is, for example, cylindrical and has a circular cross-section.

[0170] The upper portion 62 includes a lid 72 for closing the upper opening 68 and an internal structure 74 extending downwardly from the lid 72 for fitting within the lower portion 60 after the upper opening 68 is closed by the lid 72. The internal structure 74 is configured to define the separation chamber 32 and the inlet duct 34 within the interior volume 70 of the lower portion 60.

[0171] The internal structure 74 includes a partition 76 extending downwardly from the lid 72 along the central axis A to define the separation chamber 32 internally and the inlet duct 34 separated by the peripheral wall 66 externally, and a duct element 78 extending around the partition 76 to define the lower surface 50 of the inlet duct 34, the upper surface 52 of the inlet duct 34 being defined by the peripheral region of the lower surface of the lid 72.

[0172] The partition 76 has an inner surface 74A that defines a sidewall of the separation chamber 34 and an outer surface 76B that defines a sidewall of the inlet duct 34.

[0173] Looking along the central axis A, in FIG. 3, the partition 76 extends approximately 270° around the central axis A.

[0174] The inlet duct 34 is defined between the bulkhead 76 , the peripheral wall 66 , the duct element 78 and the lid 72 .

[0175] The peripheral wall 66 is provided with a connector 67 for connection to the outlet of the pyrolysis reactor 12. The outline of the connector 67 is represented in dotted lines as S to indicate its position relative to the upstream end of the inlet duct 34.

[0176] The lid 72 is perpendicular to the central axis A, the duct element 78 extends around the central axis A, and the upper surface of the duct element 78 is inclined relative to the central axis A such that the height of the inlet duct 34 gradually increases from the upstream end of the inlet duct 34 to the outlet end of the inlet duct 34 and the cross-section of the inlet duct 34 gradually increases from the upstream end of the inlet duct 34 to the outlet end of the inlet duct 34.

[0177] The duct element 78 extends, for example, helically around the central axis A of the separation chamber 32 .

[0178] When viewed along the central axis A, the partition 76 extends, for example, along a portion of a circle or along a portion of a spiral, approaching the central axis A in the downstream direction of the inlet duct 34 bounded by the partition 76.

[0179] A circular extension of the partition 76 may, for example, be used to define an inlet duct 34 of constant width in the downstream direction of the inlet duct 34, and a spiral extension of the partition 76 may, for example, be used to define an inlet duct 34 of gradually increasing width in the downstream direction of the inlet duct 34.

[0180] The bottom 64 of the lower portion 60 defines the lower surface of the separation chamber 32 .

[0181] The bottom 64 includes a discharge opening 80 for discharging impurities separated from the gas stream in the separator.

[0182] Preferably, the base 64 is shaped so that impurities fall by gravity towards the drain opening 80. As illustrated in FIG. 4, the base 64 is a frusto-conical shape that tapers downwardly towards the drain opening 80.

[0183] Optionally, separator 14 includes a collection pot 82 configured to fit beneath lower portion 60 for collecting impurities that fall into discharge opening 80 .

[0184] Preferably, the collection pot 82 is removably connected to the bottom 64. Thus, the collection pot 82 can be removed in order to empty the collection pot 82.

[0185] Optionally, the discharge opening 80 is provided with a valve 83, for example a slide valve, arranged to selectively open and close the discharge opening 80. This allows the collection pot 82 to be isolated after closing the valve 83 while the separator 14 is still in operation.

[0186] Collection pot 82 may be equipped with a gas purge line and / or may be actively cooled so that collection pot 82 may be safely removed and replaced.

[0187] In one example, the separator 14 includes a disposal device configured to discard the product accumulated in the separator 14 to a discharge opening. The disposal device is configured, for example, to discard the bottom of the separator 14.

[0188] As illustrated in FIGS. 2 and 4, the disposal device 84 is configured to, for example, dispose of product that accumulates on the bottom wall 64 of the lower portion 60 toward the discharge opening 80 .

[0189] The separator 14 is not limited to the examples illustrated in FIGS. 2-4, and other variations or options are possible.

[0190] The separator 14 of Figure 5, in which reference numbers are the same for like elements, differs from that of Figures 2-4 in that the inlet duct 34 is bounded by a lower surface 50 extending in a plane perpendicular to the central axis A, and an upper surface 52 that slopes upwardly from the upstream end of the inlet duct 34 to the downstream end of the inlet duct 34.

[0191] The separator 14 of Figure 5 differs from that of Figures 2 to 4 in that the spraying device 42 is arranged to spray the liquid monomer in the vicinity of, and in particular around, the central axis A. The spraying device 42 comprises, for example, a number of spray nozzles 44 distributed around the central axis A.

[0192] In the case where a collection tube 36 is provided as illustrated in FIG. 5, the spray device 42 is configured, for example, to spray liquid monomer around the collection tube 36 .

[0193] Spraying the liquid monomer removed from the condenser 16 into the separator 14 can be useful to prevent clogging over time of one or more mist removal grids 48 provided in the separator 14, in particular by spraying the liquid monomer onto the mist removal grids 48.

[0194] The separator 14 of FIG. 6, in which reference numbers for like elements are the same, includes a spray nozzle 44 oriented to spray the liquid monomer removed from the condenser 16 onto a downstream-most mist removal grid 48 provided in the inlet duct 34 of the separator 14.

[0195] Optionally, as illustrated in FIG. 6 , the separator 14 is provided with one or more spray nozzles 44 arranged to spray the liquid monomer removed from the condenser 16 onto the face of an upstream-most mist removal grid 48 provided in the inlet duct 34 of the separator 14.

[0196] Optionally, as illustrated in FIG. 6 , the separator 14 is provided with one or more spray nozzles 44 arranged to spray the liquid monomer removed from the condenser 16 into an intermediate space bounded between two mist removal grids 48 provided in the inlet duct 34 of the separator 14, preferably to spray the liquid monomer onto one or both of these two mist removal grids 48.

[0197] Optionally, as illustrated in FIG. 6, the separator 14 comprises a mist elimination grid 48 provided in the downstream section of the separator, in particular a mist elimination grid 48 surrounding the collection tube 36 .

[0198] The mist removal grid 48 is, for example, arranged in a tubular shape and fitted around the collection tube 36 so that the gas stream must pass through the mist removal grid to reach the collection tube 36 .

[0199] The gas stream entering separator 14 may contain solid particles due to impurities in the feedstock being depolymerized in pyrolysis reactor 12 .

[0200] Optionally, the separator 14 comprises at least one solid particle collector 90, preferably arranged in the inlet duct 34 of the separator 14, preferably upstream of a mist removal grid 48 provided in the inlet duct 34 of the separator 14.

[0201] Each solid particle collector 90 comprises, for example, a collecting pot 92 connected to the separator 14 by a collecting duct 94 so that the solid particles fall by gravity into the collecting pot 92. The collecting duct 94 connects, for example, to the lower wall 50 of the inlet duct 34 of the separator 14.

[0202] The collection pot 92 is preferably removably connected to the separator 14 so that the collection pot 92 can be emptied once the solid particles have been collected or the collection pot 92 can be replaced with a new one.

[0203] Preferably, each solid particle collector 90 is located within an environmental chamber 96 that is controlled to maintain an internal temperature above the boiling point of the monomer.

[0204] The separator 14 may include one or more solid particle collectors 90 .

[0205] As illustrated in FIG. 6, the separator 14 includes two solid particle collectors 90 each connected to the inlet duct 34 of the separator 14 at a respective location along the inlet duct 34 of the separator 14 .

[0206] When multiple solid particle collectors 90 are provided, each solid particle collector may be connected to the inlet duct 34 of the separator 14 upstream of a respective one of the multiple mist removal grids 48 provided in the inlet duct 34 of the separator 14.

[0207] As illustrated in FIG. 6 , the separator 14 includes two mist removal grids 48 extending across the inlet duct 34 of the separator 14, and two solid particle collectors 90 are respectively connected to the inlet duct 34 of the separator 14 upstream of each of these two mist removal grids 48.

[0208] One of the solid particle collectors 90 is connected to the upstream section 34 of the separator 14 upstream of the most upstream mist removal grid 48, and the solid particle collector 90 is connected to the inlet duct 34 of the separator 14 between the two mist removal grids 48.

[0209] When multiple solid particle collectors 90 are provided, they may be housed within the same environmental chamber 96 .

[0210] As illustrated in FIG. 6, the separator 14 includes two solid particle collectors 90 disposed within the same environmental chamber 96 .

[0211] 7 and 8, the separator 14 is advantageously configured with a removable inlet module 100 comprising an inlet duct 34 connected to the outlet 12B of the pyrolysis reactor 12, and an inlet tube 102 defining an inlet portion of the solid particle collector 90 connected to the inlet tube 102. The inlet module 100 preferably comprises an environmental chamber 96 attached to the inlet tube 102.

[0212] One end of the inlet pipe 102 is provided with, for example, a first flange 104 for removable connection to the remainder of the separator 14 and a second flange 106 for removable connection to the outlet 12B of the pyrolysis reactor 12.

[0213] As illustrated in FIG. 9, the separator 14 may include a mist removal grid 48 that extends across the internal flow passage 30 at the junction between the inlet duct 34 and the chamber 32 .

[0214] A mist removal grid is, for example, provided in the upper part 62 and is mounted on the bulkhead 76 and the duct element 78 .

[0215] Preferably, the mist removal grid 48 is arcuate so that it flares out in the upstream direction. The mist removal grid 48 has, for example, two straight vertical lateral edges and an arcuate upper and lower edge. This provides a larger free cross section for the passage of gas through the mist removal grid 48.

[0216] As illustrated in FIG. 9, a tubular mist removal grid 48 is also provided within the chamber 32 and around the collection tube 36 so as to cover it.

[0217] The examples were carried out in a depolymerization unit comprising a pyrolysis reactor 12 and a separator 14 and a condenser 16 .

[0218] The pyrolysis reactor 12 is provided as a twin screw extruder with co-rotating and intermeshing screws.

[0219] The twin screw extruder includes a screw extending through a barrel, an electric heater disposed about the barrel for providing heating energy, and a thermocouple disposed about the barrel for controlling temperature. The barrel may be formed, for example, by a barrel segment.

[0220] The twin screw extruder, and in particular its heater, is configured to generate a temperature profile along the screws, with a maximum profile temperature in a mid-section along the screws.

[0221] The twin screw extruder is a TEX 44 with a 47 mm screw diameter. In industrial production lines, a TEX 90 with a 96.5 mm screw diameter can be used according to the required feed rate. TEX extruders are marketed by Japan Steel Works, Ltd., which also offers larger units.

[0222] The material to be depolymerized is fed into the twin screw extruder in a hopper barrel by a gravity screw feeder. The material provided to the gravity screw feeder is pre-ground to a size of about 5-10 mm.

[0223] The twin screw extruder has along its length a depolymerization section followed by a melting section.

[0224] During operation, the material is melted in the melt zone of the twin screw extruder by shear stress from the screws and heat from the heater, and the molten material is then conveyed to the depolymerization section.

[0225] The depolymerization section of the pyrolysis reactor 12 can reach a temperature of 550° C. This generally means that the temperature in the depolymerization section of the pyrolysis reactor is equal to or lower than 550° C. Preferably, the temperature in the depolymerization section of the pyrolysis reactor is between 350° C. and 540° C., more preferably between 400° C. and 520° C., and even more preferably between 450° C. and 510° C.

[0226] In the depolymerization section, the polymer is depolymerized by heater energy assisted by shear stress (mechanical energy) from the screw and converted into MMA monomer gas, which is transferred to downstream equipment.

[0227] The PMMA mixture in the form of ground particles was fed through a gravity feeder. Two to four separate feeders contained cast, injected, and / or extruded PMMA.

[0228] During the comparative examples and the inventive examples, the following operating conditions were used: the feed rate of the material in the pyrolysis reactor 12 was comprised between 50 and 100 kg / h, the rotation speed of the screw in the pyrolysis reactor 12 was about 800 rpm, and the maximum profile temperature in the pyrolysis reactor 12 was below 500°C, or even below 490°C.

[0229] In the comparative example detailed below, separator 14 is a dead end and the gases produced during depolymerization are withdrawn through an outlet pipe located between the outlet of pyrolysis reactor 12 and separator 14.

[0230] The separator 14 is in the form of a vessel with a cylindrical side wall and a hemispherical bottom. The extrusion screw of the pyrolysis reactor 12 is oriented radially with respect to the cylindrical side wall. To avoid blockage of the reactor outlet 12B by impurities, the extrusion screw of the pyrolysis reactor 12 was inserted into the separator inlet 14A. The cylindrical vessel has an internal diameter of 817 mm and an internal height of 665 mm. The inner volume of the separator 14 is 300 liters.

[0231] The temperature of the gas in the separator 14 is measured using a thermocouple.

[0232] In the examples according to the invention detailed below, the pyrolysis reactor 12 and the condenser 16 are the same, but the separator 14 differs from that of the comparative example in that the pyrolysis reactor 12 is connected to the separator 14 such that the screw is oriented tangentially to the central axis A of the side wall 66, as in the example shown in FIG.

[0233] 3, the separator 14 is provided as a vessel with an internal partition 76 that defines the chamber 32 and the inlet duct 34 inside the vessel, the partition 76 extending around the chamber 32 from the inlet of the separator 14 to the chamber 32, the partition 76 extending along a cylindrical surface having a radius of 300 mm, and the collection tube 36 as illustrated in FIG. 2 is provided centrally within the chamber 32. The cross-sectional area of ​​the inlet duct 34 from the inlet of the separator 14 to the chamber 32 is about 344 cm. 2 ~about 470cm2 changes to.

[0234] A first thermocouple is provided to measure the temperature of the gas stream midway through the inlet duct 34 and a second thermocouple is provided near the bottom of the chamber 32 where the liquid accumulates to measure the temperature of the liquid or, if there is no liquid, to measure the temperature of the gas stream at the end of the inlet duct 34. EXAMPLES

[0235] Comparative Example 1 A pigmented mixture of cast and extruded PMMA sheets in a mass ratio of 80 / 20 was fed into the depolymerization unit. The depolymerization unit was first operated at 470°C for about 1 hour with a feed rate of 60 kg / hour. The temperature was then increased to 490°C and the depolymerization unit was operated under these conditions for 1 hour and 30 minutes. The depolymerization was stopped and restarted after 2 hours and operated at 490°C for another 1 hour and 30 minutes.

[0236] The efficiency of the condenser 16 decreased over time, as detected by the increase in temperature in the exit line. The temperature of the condensed MMA also increased and reached a maximum preset limit, at which point the pilot plant was shut down.

[0237] The condenser 16 was disassembled for inspection. The distribution plate over the condenser tubes was completely coated with black dust. Seven of the 24 tubes in the condenser 16 were completely clogged. The tubes were cleaned with a solvent for subsequent testing.

[0238] During this test, the temperature in the separator 14 varied between 30°C and 50.7°C. The temperature at the condenser inlet initially increased and stabilized between 365°C and 393°C.

[0239] The methyl methacrylate and methanol contents were determined by gas chromatography using an internal standard and calibration and were found to be 93 + / - 2 wt% and 0.4 mass%, respectively.

[0240] (Example 2 according to the present invention) The depolymerization unit was fed with cast material containing PMMA and used at feed rates of 70 and 90 kg / h for about 2 hours. Without cleaning the depolymerization unit in between, it was restarted at 500° C. and 1.5 bar, initially at a feed rate of 80 kg / h for about 30 minutes, then increased to 90 kg / h for about 1 hour, and then to 100 kg / h for the remainder of the test. The depolymerization unit was operated under these conditions at a pressure of 1.5 bar for about 30 minutes, then the pressure was reduced to 1.0 bar for 30 minutes, further reduced to 0.5 bar, and also maintained under these conditions for 30 minutes.

[0241] During this entire sequence the depolymerization plant was very stable: the condensed MMA remained below 15° C. and the temperature in the vacuum lines remained below 20° C. Measurements of the process parameters showed no signs of efficiency loss in the condenser 16.

[0242] Once the inlet side of the condenser had cooled, the depolymerization plant was inspected with an endoscope camera: the distribution plate was clean, no signs of solids buildup were found, and none of the condenser tubes were clogged.

[0243] During this test, the temperature in separator 14 measured at inlet duct 34 first rose very rapidly to 148° C., then rose to 308° C., and finally stabilized below 335° C. The temperature at the bottom of the separator first rose from 81.6° C. to 94.4° C., and stabilized below 105° C. This is an indication that the second temperature probe is in the liquid phase at the bottom of separator 14, and that MMA is either at its boiling point or may form with other impurities if one of the azeotropes is present.

[0244] The temperature at the inlet of the condenser 16 initially rose and stabilized between 250°C and 277°C.

[0245] The methyl methacrylate and methanol contents were measured by gas chromatography using an internal standard and calibration and were found to be 93 + / - 2% and 0.4% by weight, respectively (four independent measurements during the study).

[0246] Thus, in the setup according to the invention, the unit can be operated for several hours without any problems, increasing the productivity from 60 kg / h to 100 kg / h, without affecting the MMA and methanol content in the product.

[0247] Comparative Example 3 Black cast PMMA (also known as smokey cast PMMA) and white cast PMMA (used for thermoformed bathtubs) were fed into the depolymerization unit. A first feeder was used to feed the smokey cast PMMA at a feed rate of 50 kg / hr and a second feeder was used to feed the white cast PMMA at a feed rate of 50 kg / hr.

[0248] The depolymerization unit was heated at 430° C. and the smoky cast PMMA was fed for about 1 hour, followed by the white cast PMMA for about 1 hour and 20 minutes. The temperature of the depolymerization unit was then increased to 470° C. and the depolymerization unit was operated for another 60 minutes.

[0249] No indications of deviations in the operating conditions of the condenser 16 were found. Nevertheless, the condenser 16 was dismantled for visual inspection of the distribution plate and condenser tubes. A layer of fine grey-green powder had accumulated at the condenser head above the distribution plate. Gas could still flow to the condenser 16, but it was gradually clogging the depolymerization unit.

[0250] During the processing of the smoky cast PMMA, the temperature in the separator 14 varied between 24° C. and 28.8° C. The temperature at the inlet of the condenser 16 initially increased and stabilized between 280° C. and 347° C.

[0251] The methyl methacrylate and methanol contents were determined by gas chromatography using an internal standard and calibration and were found to be 96±2% and 0.2% by weight, respectively.

[0252] During the treatment of the white cast PMMA, the temperature in the separator 14 varied between 32° C. and 49.7° C. The temperature at the inlet of the condenser 16 initially increased and stabilized between 335° C. and 337° C.

[0253] The methyl methacrylate and methanol contents were determined by gas chromatography using an internal standard and calibration and were found to be 94 + / - 2% and 0.2% by weight, respectively.

[0254] (Example 4 of the present invention) The depolymerization unit was fed with smoky cast PMMA and operated at 470° C. The feed rate was first increased to 100 kg / h for 1 hour, then stabilized at 100 kg / h for 1 hour and 30 minutes to operate the depolymerization unit, then the feed rate was reduced to 90 kg / h and maintained under these conditions for 20 minutes, further reduced to 80 kg / h and maintained under these conditions for 20 minutes, then increased again to 90 kg / h and maintained under these conditions for 5 hours.

[0255] A total of 733 kg of PMMA was processed without any signs of efficiency loss. The pressure drop across the depolymerization unit was stable and the condenser 16 showed no signs of efficiency loss.

[0256] During this test, the temperature in the separator 14 at the inlet duct 34 first rose very rapidly to 141° C., then rose to 290° C., and finally stabilized below 314° C. The temperature at the bottom of the separator 14 first rose from 110° C. to 282° C., and stabilized below 299° C. This is an indication that the temperature probe is in the gas phase at the bottom of the separator 14, and that liquid phase MMA is not accumulating at the bottom of the separator 14.

[0257] The temperature at the inlet of the condenser 16 initially rose and stabilized between 261°C and 265°C.

[0258] The methyl methacrylate and methanol contents were determined by gas chromatography using an internal standard and calibration and were found to be 96 + / - 2% and 0.2% by weight, respectively (7 independent measurements during the study).

[0259] In the setup according to the invention, the unit could be operated without any problems for several hours with increasing feed rate from 50 kg / h to 90 kg / h without affecting the MMA and methanol content in the product.

[0260] The next day, 503 kg of transparent sheet extrusion material was processed under stable conditions at a feed rate of 70 kg / hr and a temperature of 470° C. for 7 hours 30 minutes (including the ramp up to stable conditions) without intermediate cleaning of the condenser 16 and separator 14. No signs of loss of efficiency of the condenser 16 were detected.

[0261] The next day the depolymerization unit was run with a controlled mixture of the exact same white cast PMMA as in Comparative Example 3, and the clear sheet extruded PMMA from the previous day. The depolymerization unit was run at a feed rate of 70 kg / hr and a temperature of 470° C.

[0262] The depolymerization unit was operated according to the following sequence: about 1 hour with pure white cast PMMA, then 1 hour with a mixture of 5% by weight clear sheet extruded PMMA and 95% by weight white cast PMMA, then 1 hour with a mixture of 10% by weight clear sheet extruded PMMA and 90% by weight white cast PMMA, then 1 hour with a mixture of 20% by weight clear sheet extruded PMMA and 80% by weight white cast PMMA, then 1 hour with a mixture of 30% by weight clear sheet extruded PMMA and 70% by weight white cast PMMA, then 1 hour with a mixture of 65% by weight clear sheet extruded PMMA and 35% by weight white cast PMMA, and finally 1 hour with 100% clear sheet extruded PMMA. A total of 572 kg of PMMA was processed during the sequence.

[0263] Finally, no signs of clogging of the depolymerization unit were detected. Nevertheless, the depolymerization unit was dismantled for inspection. Condenser 16 was filled with TiO, a pigment in white cast PMMA. 2 The unit showed slight signs of build-up of a sticky material containing . When the design of the present invention was used, the unit operated safely and stably for a much longer period of time.

[0264] During this test, the temperature in the inlet duct 34 of the separator 14 initially rose very rapidly and then stabilized between 250°C and 320°C. The temperature at the bottom of the separator 14 initially rose from 58°C to 94°C and stabilized below 147°C. This is an indication that the temperature probe is initially in the liquid phase at the bottom of the separator 14 and that the MMA is vaporizing rather than accumulating at the bottom of the separator 14. The temperature at the inlet of the condenser 16 initially rose and stabilized between 200°C and 238°C.

[0265] The methyl methacrylate and methanol contents were determined by gas chromatography using an internal standard and calibration and were found to be 97+ / -2% and 0.2% by weight, respectively.

[0266] In the setup according to the invention, the depolymerization unit could be operated without any problems for several hours while increasing the feed rate from 50 kg / h to 70 kg / h, with an improved MMA content in the product from 94% to 97% by weight.

[0267] The depolymerization method, and the corresponding depolymerization system 10 for carrying out the depolymerization method, make it possible to produce liquid monomer from a feed material containing the corresponding polymer, obtain a satisfactory purity, and maximize the operating time of the depolymerization system 10.

[0268] Indeed, the provision of separator 14 makes it possible to trap impurities that may be present in the gas stream and prevent these impurities from clogging components of the depolymerization system 10 located downstream of separator 14.

[0269] By operating the separator at a particular temperature range, any condensation and polymerization of the monomer in the separator 14 can be avoided. This further allows for spraying of cryogenic liquid monomer into the separator 14 to control the temperature of the gas stream within the separator 14.

[0270] Certain specific configurations of the separator 14, such as the limited linear velocity of the gas stream, the separation chamber 32, the inlet duct 34 having a varying cross-section and / or extending around the separation chamber 32, the collection tube 36 having a specific configuration, and / or the internal mist removal device 46, allow the temperature of the gas stream to be managed and impurities to be efficiently captured while the gaseous monomer flows to the separator outlet 14B for supply to the condenser 16.

[0271] The separator is advantageous independently of the depolymerization methods presented above.

[0272] Accordingly, the present invention also relates to a separator for a depolymerization system, the separator configured to receive a gas stream and remove impurities from the gas stream.

[0273] The separator comprises one or more of the following features, individually or in any technically feasible combination: The separator comprises a separation chamber and an inlet duct having an upstream end for receiving the gas stream and a downstream end opening into the separation chamber. - the inlet duct is configured to gradually reduce the linear velocity of the gas stream from the upstream end to the downstream end of the inlet duct; - the cross-sectional area of ​​the inlet duct increases from the upstream end to the downstream end, the inlet duct has a height that increases from its upstream end to its downstream end and / or a width that increases from its upstream end to its downstream end; - the inlet duct is bounded by a lower surface and an upper surface, the distance between the lower surface and the upper surface increasing from the upstream end to the downstream end of the inlet duct; At least one of the lower surface and the upper surface extends helically around the central axis. - the lower surface is inclined and liquid accumulating on the lower surface flows into a separation chamber; - The upper surface is inclined, - the separator comprises a discharge opening for the discharge of the product accumulated in the separator and a disposal device configured to discard the product accumulated in the separator towards the discharge opening; - a discharge opening is provided on the bottom wall of the separator; - the inlet duct extends around the separation chamber, the separation chamber being at least partially surrounded by the inlet duct; - a partition separates the inlet duct from the separation chamber; - The bulkhead is part of the cylinder, - when viewed along the central axis of the separation chamber, the partition extends along a portion of a circle or a portion of a spiral; - the separator comprises a lower and an upper portion mating with each other, the lower portion comprising a bottom and a peripheral wall extending upwardly from a periphery of the bottom wall, the peripheral wall defining an upper opening and an internal volume, the upper portion comprising a lid for closing the upper opening and an internal structure extending downwardly from the lid for insertion into the internal volume of the lower portion after the upper opening is closed by the lid and for defining an inlet duct and a separation chamber within the internal volume; - the separator comprises a collection tube extending into the separation chamber, the collection tube comprising at least one inlet section, each inlet section comprising at least one inlet opening for gas present in the separation chamber to enter the collection tube; the separator comprises baffles arranged on the collecting tube, each baffle extending around a respective inlet section; Each baffle is frusto-conical in shape, widening downwards, and each baffle has an upper end fixed to the collecting tube and a free lower end. [Explanation of symbols]

[0274] 10 Depolymerization System 12 Pyrolysis reactor 12A Reactor inlet 12B Reactor outlet, pyrolysis reactor outlet 14 Separator 14A Separator gas inlet, separator inlet 14B Separator gas outlet, separator outlet 14C Impurity outlet 16 Condenser 16A Condenser inlet, inlet, gas inlet 16B Condenser outlet, liquid outlet 16C Gas outlet 18 Monomer return line, return line 19 Reinjection Line 20 Purification Device 22 Upstream mist removal device 24 Downstream Mist Removal Device 25 Coagulant 26 Ejection Device 32 Separation chamber, chamber 34 Inlet duct, upstream section 30 Internal volume, internal flow passage 36 Collection tube 38 Inlet opening 40 Entrance Section 42 Truncated cone baffle, baffle 44 Spray nozzle 46 Internal Mist Elimination Device 48 Grid, Mist Removal Grid, Tubular Mist Removal Grid 50 Lower surface, lower surface of duct 52 Upper surface, upper surface of duct 60 Lower 62 Top 64 Bottom, bottom wall 66 Peripheral wall, side wall 67 Connector 68 Top opening 70 Internal volume 72 Lid 74 Internal structure 74A Inner surface 74B External surface 76 Bulkhead 78 Duct Elements 80 Discharge opening 82 Collection Pot 83 Valve 84 Discarded Devices 90 Solid Particle Collector 92 Collection Pot 94 Collection duct 96 Environmental Chamber 100 Removable inlet module, inlet module 102 Inlet pipe 104 First flange 106 Second flange

Claims

1. 1. A depolymerization process for recovering monomers from a polymer, comprising: - pyrolyzing a polymer-containing feedstock in a pyrolysis reactor to produce a gas stream; - directing the gas stream from the pyrolysis reactor to a separator configured to remove impurities from the gas stream; - directing the gas stream from the separator to a condenser for condensing monomers contained in the gas stream. wherein the temperature of the gas stream in the separator is maintained above the boiling point of the monomer.

2. 2. The depolymerization process according to claim 1, wherein the temperature of the gas stream in the separator is below the boiling point of the dimers of the monomer and / or below the boiling point of the trimers of the monomer, at least in the downstream section of the separator.

3. The maximum cross-sectional area of ​​the internal flow passage of the separator is at least 0.001 times the mass flow rate of the gas stream entering the separator during operation, and the area is measured in square meters (m 2 3. The depolymerization method according to claim 1, wherein the mass flow rate is expressed in kilograms per hour (kg / h).

4. 4. The method for depolymerization according to claim 1, wherein the area of ​​the largest cross-section of the internal flow passages in the separator is at least 10 times the area of ​​the smallest cross-section in the separator.

5. 5. The depolymerization process according to claim 1, wherein the linear velocity of the gas stream in the separator is less than the maximum linear velocity.

6. 6. The method of claim 5, wherein the maximum linear velocity is 0.50 m / s, in particular 0.15 m / s, or even more preferably 0.10 m / s.

7. 7. The process for depolymerization according to claim 1, wherein the maximum cross-sectional area of ​​the internal flow passages of the separator is selected as a function of the maximum feed rate of the pyrolysis reactor, the depolymerization temperature of the polymer and the molar mass of the polymer, such that the linear velocity of the gas stream in the downstream section of the inlet duct is lower than the maximum linear velocity at the maximum feed rate of the pyrolysis reactor.

8. 8. The process for depolymerization according to any one of claims 1 to 7, wherein the residence time of the gas stream in the separator is comprised between 1 s and 30 s, preferably between 5 s and 25 s, and more preferably between 10 s and 20 s.

9. 9. The method for depolymerization according to claim 1, further comprising the step of spraying liquid monomer removed from a condenser in a separator, the liquid monomer being sprayed into the gas stream.

10. 10. The method for depolymerization according to claim 9, wherein the low temperature monomer is sprayed into the separator such that the mass flow rate of the low temperature monomer sprayed into the separator accounts for 93% or less, more preferably 83% or less, more preferably 73% or less, more preferably 63% or less, and even more preferably 53% or less.

11. 11. The method for depolymerization according to claim 9 or 10, wherein the liquid monomer is sprayed into the separator such that the mass flow rate of the low temperature monomer sprayed into the separator accounts for 10% or more, more preferably 20% or more, preferably 30% or more, more preferably 40% or more, more preferably 50% or more.

12. 12. The depolymerization process according to claim 1, wherein the gas stream is gradually slowed down in the separator.

13. 13. The method for depolymerization according to claim 1, wherein the cross section of the internal flow passages of the separator increases gradually when taking into account the flow direction of the gas stream.

14. 14. The method of any one of claims 1 to 13, wherein the separator comprises a separation chamber extending along a central axis, the separator being configured such that the gas stream flows circulatingly through the separation chamber.

15. 15. The depolymerization process of claim 14, wherein the separator has an inlet duct for receiving the gas stream produced by the pyrolysis reactor, the inlet duct opening into the separation chamber.

16. 16. The depolymerization method of claim 15, wherein the inlet duct extends around the separation chamber.

17. 17. The method of any one of claims 1 to 16, comprising the step of coalescing mist droplets present in the gas stream by providing an internal mist removal device in the separator.

18. 18. The depolymerization process according to any one of claims 1 to 17, wherein the temperature in the pyrolysis reactor is 550°C or less.

19. 19. The depolymerization process according to any one of claims 1 to 18, wherein the pyrolysis reactor is a heated screw extruder, preferably a heated twin-screw extruder.

20. 20. The method for depolymerization according to any one of claims 1 to 19, wherein the polymer is a homopolymer or copolymer of methyl methacrylate (MMA) comprising at least 50% by weight, preferably at least 60% by weight, more preferably at least 70% by weight, advantageously at least 80% by weight, and even more advantageously at least 90% by weight of methyl methacrylate.

21. 21. The method of any one of claims 1 to 20, wherein the monomer is methyl methacrylate.

22. 22. The depolymerization process according to any one of the preceding claims, wherein the absolute pressure of the gas stream in the separator is comprised between 0.35 bar and 5 bar.

23. 23. The depolymerization process according to any one of claims 1 to 22, comprising the step of spraying liquid water into the separator.

24. 24. A depolymerization system configured to carry out the depolymerization method according to any one of claims 1 to 23 for recovering monomers from a polymer, comprising: - a pyrolysis reactor for pyrolyzing a polymer-containing feedstock to produce a gas stream from the feedstock; - a separator for receiving the gas stream from the pyrolysis reactor and for removing impurities from the gas stream; a condenser for receiving the gas stream from the separator for condensing monomers contained in the gas stream; and configured such that during operation, the temperature of the gas stream in the separator is maintained at or above the boiling point of the monomer.

25. 25. The depolymerization system of claim 24, wherein the pyrolysis reactor is a twin-screw extruder.

26. 26. The depolymerization system according to claim 24 or 25, configured to spray a fraction of the liquid monomer recovered by the condenser into the separator.

27. 27. The depolymerization system of any one of claims 24 to 26, comprising a reinjection line configured to collect liquid monomer at a liquid outlet of the condenser and reinject the liquid monomer into the gas inlet of the condenser.

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