Method and equipment for producing corresponding monomers by depolymerization of polymers

Abstract

The production method comprises the steps of: - pyrolyzing a feedstock in a pyrolysis reactor (4) to produce a gas stream, wherein the feedstock moves from an inlet of the pyrolysis reactor (4) to an outlet of the pyrolysis reactor (4) while being subjected to heat, and a gas stream is produced at the outlet of the pyrolysis reactor (4); and - condensing a monomer contained in the gas stream in a condenser (6) to obtain a liquid monomer, and the production method further comprises the steps of supplying the pyrolysis reactor (4) with solid and / or liquid impurities separated from the gas stream produced in the depolymerization facility (2) and / or the gas stream produced in another depolymerization facility, and / or supplying a syrup containing a polymer and / or a monomer and / or an oligomer of this monomer to the pyrolysis reactor (4).

Description

[Technical Field]

[0001] The project leading to this patent 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 the monomers are constituents.

[0003] In particular, the present invention relates to the field of depolymerization of polymethyl methacrylate (PMMA) to recover methyl methacrylate (MMA). [Background technology]

[0004] Recycled MMA can be obtained, for example, by pyrolysis of solid PMMA waste in a pyrolysis reactor, in particular in a pyrolysis reactor provided as a heated screw extruder, to obtain a gas stream comprising gaseous MMA, removing unavoidable solid and / or liquid impurities contained in this gas stream, and condensing this gas stream to obtain liquid MMA.

[0005] The liquid MMA obtained from the depolymerization of PMMA is sometimes called "crude MMA".

[0006] Additionally, some PMMA waste is a liquid product, typically a syrup that is produced to make cast PMMA sheets but cannot be used due to poor quality or changing product demands or equipment failure, and that changes too much during storage to guarantee adequate product quality when used.

[0007] With a view to improving recycling efficiency, it would be advantageous to be able to process solid and / or liquid impurities extracted from gas streams and / or liquid PMMA waste. Summary of the Invention [Problem to be solved by the invention]

[0008] One of the aims of the present invention is to provide a method for preparing a monomer, which makes it possible to obtain a monomer solution with a satisfactory purity. [Means for solving the problem]

[0009] To this end, the present invention relates to a method for producing a polymer from a feedstock containing a monomer, the method being carried out in a depolymerization facility comprising a pyrolysis reactor and a condenser, - pyrolyzing a feedstock in a pyrolysis reactor to produce a gas stream, wherein the feedstock travels from an inlet of the pyrolysis reactor to an outlet of the pyrolysis reactor while being subjected to heat, and producing a gas stream at the outlet of the pyrolysis reactor; and - condensing the monomer contained in the gas stream in a condenser to obtain liquid monomer. Including, feeding solid and / or liquid impurities separated from the gas stream produced in the depolymerization facility and / or the gas stream produced in another depolymerization facility to the pyrolysis reactor; and / or feeding a syrup containing polymer and / or monomer and / or oligomers of said monomer to the pyrolysis reactor; A method is presented, further comprising:

[0010] Syrup refers to a solution of a polymer and / or oligomer in a monomer, for example, a solution of PMMA or MMA oligomers in MMA. The syrup can be obtained by prepolymerization of a monomer, for example, MMA, as is commonly done, for example, in the production of cast PMMA sheets. Alternatively, the syrup can be obtained, for example, by dissolving a polymer in a monomer, for example, PMMA in MMA. In the latter case, it is preferable to use a polymer grade with a lower molecular weight, for example, a PMMA grade with a lower molecular weight, which may have better solubility.

[0011] The solid and liquid impurities separated from the gas stream produced in the pyrolysis reactor may include depolymerization residues mixed with some monomers, such as MMA. Solid impurities include, for example, fine dust of pigments and their decomposition products, contaminating polymers, reinforcing agents such as glass and carbon fibers, wood residues, monomers and oligomers from other polymers, and their decomposition products if they are insoluble in the liquid medium. Liquid impurities may include not only the monomer and its oligomers, but also the polymer fraction soluble in the monomer, all decomposition products from the polymer itself, and its contaminants. To some extent, the liquid impurities may contain water, hydrocarbons, such as decomposition products from polyethylene film covering PMMA sheets, aromatics, such as toluene and xylenes, and some heavy aromatics produced not only by the decomposition of polymers and contaminants but also from the decomposition of additives, such as impact additives. In reality, the majority of the liquid and solid impurities are composed not only of monomers, dimers, and trimers, and decomposition products, but also of combinations of monomers and comonomers and their decomposition products, as well as solutions of polymers and oligomers.

[0012] In certain embodiments, the manufacturing method comprises one or several of the following optional features, individually or in any technically feasible combination: - feeding solid and / or liquid impurities into the pyrolysis reactor, preferably in a section of the pyrolysis reactor close to the outlet of the pyrolysis reactor, in particular closer to the outlet than to the inlet; the intermediate section, in which solid and / or liquid impurities are fed to the pyrolysis reactor, is at a temperature below 300°C, preferably below 250°C, more preferably below 200°C, and / or above the boiling point of the monomer and / or above 100°C; - feeding the syrup into the pyrolysis reactor, preferably in close proximity to the inlet of the pyrolysis reactor, in particular in an intermediate section of the pyrolysis reactor closer to the inlet than to the outlet; - the intermediate section in which the syrup is fed to the pyrolysis reactor is at a temperature below 450°C, preferably below 350°C, more preferably below 300°C, even more preferably below 250°C; - Injecting solid polymer into the pyrolysis reactor to create a solid plug between the injection point of the syrup and the inlet of the pyrolysis reactor; the temperature in the intermediate section of the pyrolysis reactor, located between the injection point of the syrup and the injection points of the solid and liquid impurities, is above 250°C, preferably above 350°C, in particular above 400°C; - the pyrolysis reactor is a heated screw extruder comprising an elongated barrel defined by a series of barrel sections connected in series and at least one screw extending within the barrel for conveying a feed material along the barrel, each barrel section being provided with a respective heating device for heating the section of the barrel corresponding to that barrel section, the inlet being located within the first barrel section of the series and the outlet being located within the last barrel section of the series; - solid impurities and / or liquid impurities are provided in the third to last barrel section, the second to last barrel section, and / or the last barrel section; - the method comprises the step of separating solid and / or liquid impurities from the gas stream in a separation unit before feeding the gas stream to a condenser; - the method includes a step of scrubbing the gas stream between the separation unit and the condenser using a gas scrubbing unit fluidly connected in series between the separation unit and the condenser, the gas scrubbing unit comprising a transfer column including internal parts, the gas scrubbing unit being supplied with cold monomer in a liquid state, so that the gas stream flows upward in the transfer column, the cold monomer flows downward in the transfer column by gravity, and heavy contaminants contained in the gas stream condense in a liquid state in the internal parts and flow down by gravity towards the bottom of the transfer column, and then transferred to the separation unit; - The cold monomer injected into the transfer column is part of the monomer solution recovered from the outlet of the condenser; - the separation unit comprises a main separator and an auxiliary separator fluidly connected in series; - The monomer is methyl methacrylate (MMA) and the polymer is poly(methyl methacrylate) (PMMA).

[0013] The present invention also relates to an installation for producing a monomer from a feed containing a polymer composed of said monomers, said installation comprising a pyrolysis reactor and a condenser, and adapted to carry out the production method defined above.

[0014] The invention and its advantages will be better understood on reading the following description, given purely by way of non-limiting example and given with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic diagram illustrating a depolymerization facility for producing a monomer solution from a feed containing a polymer composed of monomers. [Figure 2] FIG. 1 is a schematic diagram illustrating a pyrolysis reactor configured as a heated screw extruder. DETAILED DESCRIPTION OF THE INVENTION

[0016] The depolymerization facility 2 of FIG. 1 is configured to produce monomers from a feed material F containing polymers composed of monomers.

[0017] The depolymerization facility 2 comprises a pyrolysis reactor 4 configured to receive a feedstock and produce a gas stream G containing the monomers in a gaseous state, and a condenser 6 configured to condense the gas stream G to obtain a monomer solution M containing the monomers in a liquid state.

[0018] In the following, the monomer solution M obtained from the condensation of the gas stream G is also called "crude monomer solution" or "crude monomer" or "liquid monomer".

[0019] Pyrolysis reactor 4 is advantageously a heated screw extruder comprising a heated barrel 8 and at least one screw 10 disposed within barrel 8 for moving the feed material through barrel 8 while heating the feed material.

[0020] The depolymerization facility 2 preferably comprises a feeder 12 configured to feed the feedstock F to the inlet 4A of the pyrolysis reactor 4.

[0021] The depolymerization facility 2 optionally comprises a separation unit 14 fluidly connected in series between the outlet 4B of the pyrolysis reactor 4, which supplies the gas stream G, and the inlet of the condenser 6, the separation unit 14 being configured to separate solid and / or liquid impurities from the gas stream G before supplying the gas stream G to the condenser 6.

[0022] The separation unit 14 comprises a primary separator 16 configured, for example, to reduce the linear velocity of the gas stream G to facilitate separation and deposition of solid impurities, and / or to demist the gas stream G to facilitate deposition of mist droplets of liquid impurities, and / or to scrub the gas stream with a scrubbing liquid to facilitate deposition of liquid impurities.

[0023] The reduction in the linear velocity of the gas flow G can be achieved, for example, by gradually increasing the cross-sectional area of ​​the internal flow passage of the main separator 16 through which the gas flow G passes within the main separator 16.

[0024] Preferably, the primary separator 16 is configured such that the internal flow path of the primary separator 16 is not linear, which promotes separation and deposition of impurities.

[0025] Mist removal of the gas flow G is achieved, for example, by providing one or several mist removal grids throughout the internal flow path of the primary separator 16 .

[0026] Washing of gas stream G is accomplished, for example, by injecting water and / or liquid monomer into the internal flow passages of primary separator 16 .

[0027] Separation unit 14 optionally includes an auxiliary separator 18 disposed upstream of main separator 16. Gas stream G produced by pyrolysis reactor 4 flows through auxiliary separator 18 before entering main separator 16.

[0028] The auxiliary separator 18 is configured to remove solid impurities from the hot gas stream G by inertia, for example.

[0029] The auxiliary separator 18 is configured, for example, with an internal flow passage located above the collection pot and having a change in cross section that promotes a reduction in linear velocity and / or a change in direction, so that solid particles slowed down by the reduction in linear velocity and / or carried by inertia tend to collide with the walls of the internal flow passage and fall into the collection pot.

[0030] Advantageously, the depolymerization installation 2 comprises a gas washing unit 20 connected in series between the separation unit 14 and the condenser 6 and configured to remove heavy substances from the gas stream G before the gas stream enters the condenser 6.

[0031] The gas washing unit 20 is arranged so that the gas stream G exiting the separation unit 14 passes through the gas washing unit 20 before entering the condenser 6 .

[0032] The gas scrubbing unit 20 comprises a transfer column 22 extending upwardly between a lower end 22A and an upper end 22B. The lower end 22A is fluidly connected to the separation unit 14, particularly the main separator 16, for receiving the gas stream G exiting the separation unit 14. The upper end 22B is fluidly connected to the inlet 6A of the condenser 6.

[0033] The gas scrubbing unit 20 comprises a reinjection loop 24 configured to reinject a portion of the monomer solution recovered at the outlet 6B of the condenser 6 into the top of the transfer column 22, in particular into the top end 22B of the transfer column 22.

[0034] Transfer column 22 includes internal components, such as baffles, structured packing, gauze packing, and / or random packing, such as random packing including saddles and / or rings, particularly pall rings.

[0035] The internals are configured such that, during operation, the gas stream flows upward within the transfer column 22, the temperature of the gas stream decreases along the transfer column 22, the monomer solution injected into the transfer column 22 flows downward within the transfer column 22 by gravity, and the heavy contaminants H contained in the gas stream condense on the internals and flow back up the transfer column 22 in a liquid state into the separation unit 14, particularly into the main separator 16.

[0036] The depolymerization facility 2 optionally comprises a purification unit 26 configured to purify the monomer solution to obtain a purified monomer solution M containing fewer impurities.

[0037] The purification unit 26 may comprise, for example, an evaporator-condenser unit configured to continuously evaporate and condense the monomer solution while removing heavy materials in an evaporator, a crystallization unit comprising one or several distillation columns, thin film evaporators, short path distillation units, and / or one or several crystallizers configured to perform fractional crystallization, or any other suitable technique or combination of techniques for purifying the monomer solution.

[0038] The facility 2 is configured to supply the pyrolysis reactor 4 with solid and / or liquid impurities R separated from the gas stream G produced in the depolymerization facility 2 and / or from a gas stream produced in another depolymerization facility, and / or with a syrup S containing a polymer and / or a monomer and / or an oligomer of this monomer.

[0039] The depolymerization facility 2 includes, for example, a reinjection line 30 configured to supply the pyrolysis reactor 4 with solid and / or liquid impurities R separated from the gas stream produced in the depolymerization facility 2 and / or the gas stream produced in another depolymerization facility.

[0040] For example, the reinjection line 30 connects the separation unit 14 to the pyrolysis reactor 4 for injecting into the pyrolysis reactor 4 solid and / or liquid impurities R separated from the gas stream G in the separation unit 14, and / or connects another separation unit 34 of another depolymerization facility to the pyrolysis reactor 4 for injecting into the pyrolysis reactor 4 solid and / or liquid impurities separated from the gas stream in this other separation unit 34.

[0041] In particular, the reinjection line 30 connects the main separator 16 of the separation unit 14 to the pyrolysis reactor 4 and / or connects the main separator of another separation unit 34 to the pyrolysis reactor 4 .

[0042] The depolymerization facility 2 comprises an injection line 36 configured to supply syrup S to the pyrolysis reactor 4, for example, from a syrup source 38, such as a syrup container.

[0043] The barrel 8 is preferably configured to heat the material contained within the barrel 8 according to a temperature profile, ie, a temperature that varies along the barrel 8 .

[0044] Preferably, the pyrolysis reactor 4 is configured to produce a temperature profile that gradually increases and then gradually decreases from the inlet of the pyrolysis reactor 4 that receives the feedstock to the outlet of the pyrolysis reactor 4 that delivers the gas stream.

[0045] Typically the temperature profile will have an inlet temperature greater than 100°C, a maximum temperature greater than 250°C, particularly greater than 350°C, more particularly greater than 400°C, and an outlet temperature greater than 100°C.

[0046] Preferably, the solid and liquid impurities are fed to the pyrolysis reactor 4 in close proximity to the outlet 4B of the pyrolysis reactor 4, particularly closer to the outlet 4B than to the inlet 4A, i.e., in a section of the pyrolysis reactor 4 in the latter half of the length of the barrel 8 of the pyrolysis reactor 4.

[0047] The section of the pyrolysis reactor 4 where the solid and liquid impurities R are fed to the pyrolysis reactor 4 is preferably at a temperature below 300°C, preferably below 250°C, more preferably below 200°C.

[0048] The section of the pyrolysis reactor 4 where the solid and liquid impurities R are fed to the pyrolysis reactor 4 is preferably at a temperature above 100° C. or above the boiling point of the monomer.

[0049] Preferably, the syrup is fed to a section of the pyrolysis reactor 4 in close proximity to the inlet 4A of the pyrolysis reactor 4, particularly closer to the inlet 4A than to the outlet 4B, i.e., in the first half of the length of the barrel 8 of the pyrolysis reactor 4.

[0050] The section of the pyrolysis reactor 4 where the syrup S is fed to the pyrolysis reactor 4 is preferably at a temperature below 450°C, more preferably below 350°C, more preferably below 300°C, preferably below 250°C.

[0051] If both solid and / or liquid impurities R and syrup S are injected into the pyrolysis reactor 4, they are preferably injected into separate compartments of the pyrolysis reactor 4. The injection point of the solid and / or liquid impurities R into the pyrolysis reactor 4 is separate and distinct from the injection point of the syrup S into the pyrolysis reactor 4.

[0052] Preferably, the feed material is injected into the pyrolysis reactor 4 to create a solid plug between the injection point of the syrup S into the pyrolysis reactor 4 and the inlet 4A of the pyrolysis reactor 4 that receives the feed material F. In particular, the feed material F comprises or consists of solid material.

[0053] The presence of the plug in the pyrolysis reactor 4 prevents gaseous MMA and other decomposition products, solid and / or liquid impurities, and / or syrup from flowing back through the pyrolysis reactor 4 toward the inlet 4A that receives the feedstock F.

[0054] Preferably, the pyrolysis reactor 4 is configured so that the temperature in the section of the pyrolysis reactor 4 located between the injection point of the syrup S and the injection point of the solid and / or liquid impurities R is above 250°C, preferably above 350°C, in particular above 400°C.

[0055] 2, the barrel 8 of the pyrolysis reactor 4 is defined, for example, by a series of barrel sections 40 (also called "barrel cylinders") connected in series, each barrel section 40 being provided with a respective heating device 42 for heating that particular barrel section 40. Each barrel section 40 (or barrel cylinder) defines a portion of the length of the barrel 8.

[0056] Pyrolysis reactor 4 includes, for example, an electrical control unit 44 configured to individually control heating devices 42 of barrel sections 40 to generate a desired temperature profile within barrel 8 .

[0057] Preferably, the inlet of the pyrolysis reactor 4 that receives the feedstock is located in the first barrel section 40 of the series of barrel sections 40, and / or the outlet of the pyrolysis reactor 4 that delivers the gas stream G is located in the last barrel section 40 of the series of barrel sections 40.

[0058] Preferably, the solid impurities and / or liquid impurities R are provided in the third to last barrel section 40, the second to last barrel section 40, and / or the last barrel section 40 of the series of barrel sections 40.

[0059] As shown in FIG. 2, solid and / or liquid impurities R are fed into the penultimate barrel section 40 in the series of barrel sections 40 .

[0060] As shown in FIG. 2, the syrup is fed to the second barrel section 40 in the series of barrel sections 40.

[0061] This is merely an example. In practice, the barrel section 40 into which the syrup is injected will be selected depending on the operating conditions.

[0062] The syrup may be injected, for example, in the second barrel section, the third barrel section, the fourth barrel section, the fifth barrel section, or the sixth barrel section.

[0063] During operation, the depolymerization facility 2 - pyrolyzing a feedstock F in a pyrolysis reactor 4 to produce a gas stream G, the feedstock F moving from an inlet 4A of the pyrolysis reactor 4 to an outlet 4B of the pyrolysis reactor 4 and being subjected to heat to produce a gas stream G at the outlet of the pyrolysis reactor 4; and - condensing the monomer contained in the gas stream in a condenser 6 to obtain liquid monomer M The method is configured to perform a depolymerization method, including:

[0064] The production method further comprises the step of feeding the pyrolysis reactor 4 with solid and / or liquid impurities R separated from the gas stream G produced in the depolymerization facility 2 and / or from a gas stream produced in another depolymerization facility, and / or the step of feeding the pyrolysis reactor 4 with a syrup S containing a polymer and / or a monomer and / or an oligomer of this monomer.

[0065] If applicable, solid and / or liquid impurities R are preferably supplied to the pyrolysis reactor 4 in a section of the pyrolysis reactor 4 that is proximate to the outlet 4B of the pyrolysis reactor 4, in particular closer to the outlet 4B than to the inlet 4A.

[0066] The section of the pyrolysis reactor 4 where the solid and liquid impurities R are fed to the pyrolysis reactor 4 is preferably at a temperature below 300°C, preferably below 250°C, more preferably below 200°C.

[0067] The section of the pyrolysis reactor 4 where the solid and liquid impurities R are fed to the pyrolysis reactor 4 is preferably at a temperature above the boiling point of the monomer and / or above 100°C.

[0068] If applicable, the syrup S is preferably fed to a section of the pyrolysis reactor 4 adjacent to the inlet 4A of the pyrolysis reactor 4, in particular closer to the inlet 4A than to the outlet 4B.

[0069] The section of the pyrolysis reactor 4 where the syrup S is fed to the pyrolysis reactor 4 is at a temperature below 450°C, more preferably below 350°C, more preferably below 300°C, preferably below 250°C.

[0070] Preferably, the depolymerization method includes the step of creating a solid plug between the injection point of the syrup S into the pyrolysis reactor 4 and the inlet 4A of the pyrolysis reactor 4 that receives the feedstock F.

[0071] Feedstock F is preferably fed into a first barrel section 40 of a series of barrel sections 40 forming barrel 8 .

[0072] Preferably, the solid impurities and / or liquid impurities R are provided in the third to last barrel section 40, the second to last barrel section 40, and / or the last barrel section 40 of the series of barrel sections 40.

[0073] The syrup S is supplied to a barrel section included between the second barrel section 40 and the sixth barrel section 40 of the series of barrel sections 40, for example.

[0074] Preferably, the temperature of gas stream G at the outlet of main separator 16 and the inlet of transfer column 22 is maintained at at least the boiling point of the monomer, particularly at least the boiling point of the monomer + 10°C, particularly at least the boiling point of the monomer + 20°C, particularly at least the boiling point of the monomer + 30°C, more particularly at least the boiling point of the monomer + 40°C, and even more particularly at least the boiling point of the monomer + 50°C.

[0075] Preferably, the gas stream G at the outlet of the transfer column 22 is maintained between the boiling point of the monomer and the boiling point of the monomer + 50°C, in particular between the boiling point of the monomer and the boiling point of the monomer + 40°C, in particular between the boiling point of the monomer and the boiling point of the monomer + 30°C, in particular between the boiling point of the monomer and the boiling point of the monomer + 20°C, in particular between the boiling point of the monomer and the boiling point of the monomer + 10°C.

[0076] The monomer is, for example, methyl methacrylate (MMA) and the polymer is poly(methyl methacrylate) (PMMA).

[0077] The provision of a separation step carried out in the separation unit 14 and a washing step carried out in the washing unit 20 makes it possible to improve the quality of the monomer solution obtained.

[0078] The solid and / or liquid impurities R separated from the gas stream G produced by the pyrolysis reactor 4 of the depolymerization facility 2 or a pyrolysis reactor of another depolymerization facility generally contain a variety of molecules, including monomers (e.g., MMA), oligomers, additives, decomposition products, solid residues from the polymer (e.g., PMMA), and other polymers that have contaminated the polymer contained in the feed, and also including termination by-products.

[0079] By returning the solid and / or liquid impurities R, including the monomers, to the pyrolysis reactor 4, it is possible to increase the yield by recovering the monomers and depolymerized polymer contained in the solid and / or liquid impurities R separated from the gas stream G.

[0080] In particular, it appears more appropriate to return the solid and / or liquid impurities R into the section of the pyrolysis reactor 4 at a limited temperature, in particular below 300°C, preferably below 250°C, preferably below 200°C.

[0081] Syrup S is difficult to recycle, and injecting the syrup S into the pyrolysis reactor 4 makes it possible to recycle the syrup. Syrup S is more efficiently recycled by injecting the syrup into an upstream section of the pyrolysis reactor 4 so that the syrup is subjected to a temperature profile, in particular a gradually increasing and then gradually decreasing temperature.

[0082] Unexpectedly, when syrup is fed into the pyrolysis reactor 4, it is possible to depolymerize more of the feedstock than when only the feedstock is depolymerized.

[0083] For the same amount of energy consumed in the pyrolysis reactor 4, a higher total mass flow can be processed if syrup is fed into the pyrolysis reactor 4 in addition to the feedstock.

[0084] The pyrolysis reactor 4, which is provided as a heated screw extruder, uses mechanical and thermal energy to depolymerize the polymer.

[0085] When the syrup S is injected into the pyrolysis reactor 4, it is expected that the mechanical energy requirements will be reduced.

[0086] Unexpectedly, the mechanical energy requirement remains stable, however, as more mechanical energy is provided in the first barrel section 40 of barrel 8 and the polymer melts, less mechanical energy is required and more thermal energy is required.

[0087] Therefore, the injection point of the syrup S should be appropriately selected so that at the injection point of the syrup S, the feed material F is already melted and the viscosity of the molten polymer is sufficiently reduced so that most of the mechanical energy has been consumed.

[0088] In practice, depending on the length of the barrel 8 and the number of barrel sections 40, this will often correspond to a barrel section 40 included between the second barrel section 40 and the sixth barrel section 40 of the series of barrels 40 of the barrel 8.

[0089] In this production method, the injection of solid impurities and / or liquid impurities and syrup into the pyrolysis reactor 4 is operated, for example, continuously at a constant or variable rate, or intermittently, such as by alternating injection and non-injection phases. Variable rate and / or intermittent injection makes it possible to operate at higher speeds during high-speed or injection phases, which may make operation easier. [Example]

[0090] In Examples 1 to 3, syrup was injected into the pyrolysis reactor 4.

[0091] Examples 1 to 3 were carried out in a depolymerization facility 2 equipped with a pyrolysis reactor 4, a condenser 6, a feeder 12, a separation unit 14, and a gas scrubbing unit 20.

[0092] The pyrolysis reactor 4 was provided as a twin-screw extruder comprising a barrel 8 and two parallel screws 10 with co-rotating and intermeshing screws 10. The barrel 8 was made up of a series of barrel sections 40. A heater 42 was provided to generate a temperature profile along the barrel 8, which gradually increased and then decreased along the barrel 8, with a maximum profile temperature at the middle section of the barrel 8.

[0093] More specifically, the twin-screw extruder was a TEX44 with a 47 mm screw diameter. For industrial production lines, a TEX90 with a 96.5 mm screw diameter may be used depending on the required feed rate. TEX extruders are sold by The Japan Steel Works Ltd., which also offers larger units.

[0094] In operation, pyrolysis reactor 4 had a melting section followed by a depolymerization section along the length of barrel 8. Feedstock F was melted in the melting zone of pyrolysis reactor 4 by shear stress from screw 10 and heat from heater 42, and the molten material was then transported to the depolymerization section. The depolymerization section of pyrolysis reactor 4 can reach temperatures of 550°C.

[0095] The condenser 6 was provided as a tube-shell heat exchanger.

[0096] The feeder 12 was a mass-feed screw feeder 12 .

[0097] The separation unit 14 consisted of a main separator 16. The separation unit 14 did not include an auxiliary separator 18 located upstream of the main separator 16.

[0098] The transfer between the separation unit 14 and the condenser 6 was carried out via a transfer column 22 having an inner diameter of 5.08 cm and an internal part as a filter mesh. The filter mesh was a cylindrical grid with holes having a diameter of 1 mm. The filter mesh was inserted at an angle within the transfer column 22 so that the gas stream G was filtered through the filter mesh. The filter mesh was located in the upper part of the transfer column 18, closer to the condenser 6 than to the separation unit 14.

[0099] The filter mesh was operated "dry", ie, without reinjecting the monomer solution into the transfer column.

[0100] Pyrolysis reactor 4 consists of barrel 8 made up of a series of 17 barrel sections, hereinafter referred to as barrel section #1 through barrel section #17, and is equipped with an injection port for injecting MMA syrup located at barrel section #5.

[0101] Table 1 below shows the configuration of the pyrolysis reactor 4, in particular the function of each barrel section 40 and the set temperature of each barrel section 40 during the implementation of Examples 1, 2, and 3.

[0102] [Table 1]

[0103] Barrel sections #16 and #17 are set at 250°C, but the actual temperature is usually higher due to heat transfer from the previous barrel section and hot gases.

[0104] The feed material used was cast transparent PMMA sheet that was ground into particles having a size of approximately 5-10 mm.

[0105] The syrup was a PMMA syrup containing white pigment. The syrup had been produced several days earlier and was leftover from cast sheet production. The syrup had an acceptable viscosity for pumping into pyrolysis reactor 4. The syrup was stored in a tank at room temperature and under a controlled atmosphere. The syrup was pumped from the tank to pyrolysis reactor 4 using a dosing pump capable of delivering up to 30 kg / h.

[0106] The feed was depolymerized at 470°C in the pyrolysis reactor 4 with a feed rate that was increased from 0 to 100 kg / h, and the first sample of MMA solution was taken after 25 minutes of operation at 100 kg / h (Example 1a).

[0107] The feed rate was then reduced to 90 kg / h and after 30 minutes of stabilization a second sample of the MMA solution was taken (Example 1b).

[0108] The feed rate was then reduced to 80 kg / h and syrup injection was initiated at 10 kg / h in the fifth barrel section (barrel section #5). No significant changes in the screw temperature profile were recorded. After stabilization, a sample of the MMA solution was taken (Example 2).

[0109] After 30 minutes of operation, the feed rate was kept at 80 kg / h and the syrup injection was increased to 30 kg / h and after stabilization a new sample of the MMA solution was taken (Example 3).

[0110] During the run of Examples 1 and 2, the temperature in barrel section #6 was 455°C and 453°C, respectively. In Example 3, the temperature in barrel section #6 dropped to 413°C during the run of Example 3. Additionally, the temperatures in barrel sections #7 and #8 were affected by less than 10°C, which was not significant, and the temperature in barrel section #9 was not affected.

[0111] The samples taken in Examples 1a, 1b, 2, and 3 were analyzed by gas chromatography to determine the MMA content and some important impurity contents of the MMA solutions.

[0112] As can be seen in Table 2 below, which shows the results of the analysis, the MMA content remained at about 95-96 wt%. The methanol and methyl isobutyrate contents remained in the same range. Methyl acrylate and ethyl acrylate were comonomers present in the cast PMMA used as feedstock. Their content decreased because PMMA scrap was partially replaced with syrup that did not contain these comonomers. The decrease in ethyl acrylate from Examples 1a and 1b to Examples 2 and 3 followed a linear correlation and was not due to artifact.

[0113] [Table 2]

[0114] The amount of heavy materials in the MMA solution (or "crude MMA") was estimated by gas chromatographic analysis of products with much longer retention times than MMA. Replacing a portion of the PMMA scrap (feed material) with MMA syrup slightly reduced the amount of heavy materials, determined as a percentage of the gas chromatographic peak area of ​​the detected products.

[0115] These examples demonstrate that it was possible to replace significant amounts of PMMA scrap with MMA syrup without adversely affecting the quality of the crude MMA. In this case, there was no increase in heavy materials, indicating that the MMA oligomers present in the syrup did not affect the purity of the crude MMA.

[0116] The productivity of the depolymerization plant is increased. When only PMMA scrap was used, the maximum productivity of the depolymerization plant was limited to 100 kg / h under the same conditions. However, by replacing 20 kg / h of PMMA scrap with MMA syrup, it was possible to supply 30 kg / h of syrup while maintaining the plant's performance.

[0117] Examples 4, 5, and 6 can be contemplated using a pyrolysis reactor 4 configured with syrup injection ports located in barrel sections #12, #15, and #16, respectively, rather than barrel #5.

[0118] In the above cases 4, 5 and 6, the amount of syrup to be injected is limited by visual detection of the non-depolymerized fraction at the outlet 4B of the pyrolysis reactor 4 or in the separation unit 14. The MMA syrup feed rate will then be adjusted to the maximum amount and the depolymerization equipment will then be stabilized for data acquisition.

[0119] Table 3 below shows the expected results for Examples 4-6.

[0120] [Table 3]

[0121] According to these predicted results in Table 3, if the MMA syrup is injected into the downstream half of barrel 8, the productivity of the depolymerization facility will decrease and the maximum amount of MMA syrup that can be injected into the pyrolysis reactor 4 will be limited.

[0122] It is envisaged that it is preferable to inject the syrup into an upstream section of barrel 8 of pyrolysis reactor 4, in particular the section upstream of the section of maximum profile temperature.

[0123] Examples 7 to 12 can be implemented in particular by providing a gas scrubbing unit 20 and reinjecting the liquid heavy materials recovered in the main separator 16 into the pyrolysis reactor 4. The depolymerization facility 2 would therefore be modified as follows: a) An auxiliary separator 18 is added to the separation unit 14. This auxiliary separator 18 is intended to capture solid dust and incompletely depolymerized PMMA exiting the pyrolysis reactor 4. The auxiliary separator 18 comprises a duct for circulating the gas flow, the duct having a circular cross section with an inner diameter of 400 mm, a horizontal gas inlet section connected to the outlet 4B of the pyrolysis reactor 4, and a horizontal gas outlet section connected to the main separator 16, the gas outlet being located 500 mm higher than the gas inlet, the duct having an intermediate section extending vertically upward from the gas inlet section to the gas outlet section, and a collector at the lower end of the intermediate section. The auxiliary separator 18 is intended to reduce the gas velocity in the intermediate section so that dust falls to the bottom of the intermediate section and is collected in the collector. The auxiliary separator 18 is intended to be preheated to above 100°C to prevent condensation of MMA.

[0124] b) The primary separator 16 is configured so that the gas flows along a spiral path towards a central chamber, allowing any remaining dust to settle within the spiral path. The gas is collected via a collection pipe extending centrally within the chamber and exits the primary separator 16. A first mist removal grid with holes having a diameter of 8 mm is provided within the spiral path, and a second mist removal grid with holes having a diameter of 3 mm is provided in the central chamber around the collection pipe.

[0125] c) A gas cleaning unit 20 is added, which comprises a vertical transfer column 22 having an internal diameter of 200 mm and two compartments located one above the other. The two compartments are filled with packing material (cylindrical packing with 16 mm Pall rings, wall thickness of 0.3 mm, 385 kg / m 3 Mass of 214,000 pieces / m 3 , 344m 2 / m 3 , manufactured by MTE Group, Boezemweg 5, 3255 MC Oude-Tonge, The Netherlands). The two compartments have a total packing height of 2 metres.

[0126] d) The condenser 6 is modified by adding two grids with holes having a diameter of 2 mm, spaced 5 cm apart and stacked on top of each other, the two grids being placed on top of the tubes to distribute the gas over the tubes.

[0127] e) Add a re-injection loop 24 to inject MMA solution from the bottom of the condenser 6 into the upper section 22B of the transfer column 22 at an adjustable rate.

[0128] f) The primary separator 16 and the transfer column 22 are fluidly connected such that the heavier materials flowing to the bottom of the transfer column 22 are returned to the primary separator 16 .

[0129] g) Adding a re-injection loop 30 to recover the heavy materials in the primary separator 16 and re-inject these heavy materials into the pyrolysis reactor 4.

[0130] The following adjustable parameters are expected to affect the quality of crude MMA and the yield of depolymerization:

[0131] 1) The flow rate of crude MMA returned to the top of the transfer column 22. This can affect not only the temperature at the inlet of the condenser 6 and the temperature at the top of the transfer column 22, but also the temperature at the bottom of the transfer column 22. This can also affect the amount of liquid that must be reinjected into the pyrolysis reactor 4.

[0132] 2) The flow rate of liquid heavy materials re-injected into the pyrolysis reactor 4.

[0133] 3) The temperature at the outlet 4B of the pyrolysis reactor 4. By providing more heat downstream of the injection of the liquid heavy materials, it is possible to make it possible to vaporize more heavy materials.

[0134] For Examples 7, 8, and 9, the feed material will be injection-grade PMMA products from automobile taillights collected at salvage yards that process end-of-life vehicles to be crushed into small particles. These PMMA scraps are generally mixed in color (red, black, clear, orange...) and are also contaminated with other polymers such as polycarbonate and ABS.

[0135] The PMMA scrap will be fed at a rate of 50 kg / h into the pyrolysis reactor 4, which will be operated at a maximum profile temperature of 470°C and a screw rotation speed of 800 rpm, and the return flow of crude MMA from the condenser 6 to the gas washing unit 20 will be adjusted to about 50 kg / h.

[0136] Barrel 8 of Pyrolysis Reactor 4 will be fitted with an injection port located in barrel section #16 for injecting liquid heavies recovered from Separation Unit 14. Pyrolysis Reactor 4 will therefore be configured as shown in Table 4 below.

[0137] [Table 4]

[0138] The expected results are shown in table 6 below.

[0139] [Table 5]

[0140] For Examples 10, 11, and 12, the liquid injection ports would be moved to barrel sections #5, #9, and #12, respectively. The barrel section prior to the barrel section with liquid injection would be cooled to 250° C. Pyrolysis reactor 4 would be reconfigured for each example.

[0141] For example, pyrolysis reactor 4 for Example 12 would be configured as shown in Table 5 below.

[0142] [Table 6]

[0143] In the cases of Examples 10, 11, and 12, the heavy materials are expected to adversely affect the quality of the crude MMA produced. The amounts of impurities such as methyl isobutyrate, methyl acrylate, and ethyl acrylate are expected to increase. [Explanation of symbols]

[0144] 2 Depolymerization equipment 4. Pyrolysis reactor Entrance 4A 4B Exit 6. Condenser 6A entrance 6B Exit 8 barrels 10 screws 12 Feeding machine 14 Separation Unit 16 Main separator 18 Auxiliary separator 20 Gas Cleaning Unit 22 Transfer column 22A lower end 22B Upper edge 24 Reinfusion Loop 26 Refining Unit 30 Reinfusion Line 34 Separation Unit 36 Infusion Line 38 Syrup Sources 40 barrel compartment 42 Heating Devices 44 Electrical Control Unit F Feed material G Gas flow M monomer solution R Solid impurities and / or liquid impurities S syrup

Claims

1. A method for producing a polymer from a feedstock containing a monomer, the method being carried out in a depolymerization facility (2) comprising a pyrolysis reactor (4) and a condenser (6), - pyrolyzing the feedstock in a pyrolysis reactor (4) to produce a gas stream, the feedstock moving from an inlet of the pyrolysis reactor (4) to an outlet of the pyrolysis reactor (4) while being subjected to heat, to produce a gas stream at the outlet of the pyrolysis reactor (4); and - condensing the monomer contained in the gas stream in a condenser (6) to obtain liquid monomer. Including, feeding the pyrolysis reactor (4) with solid and / or liquid impurities separated from the gas stream produced in the depolymerization facility (2) and / or the gas stream produced in another depolymerization facility; and / or feeding a syrup containing the polymer and / or the monomer and / or an oligomer of the monomer into a pyrolysis reactor (4); The method further comprises:

2. 2. The process according to claim 1, wherein the solid and / or liquid impurities are fed to the pyrolysis reactor (4), preferably in a section of the pyrolysis reactor (4) close to the outlet of the pyrolysis reactor (4), in particular closer to the outlet than to the inlet.

3. 3. The process according to claim 2, wherein the intermediate section, in which solid and / or liquid impurities are fed to the pyrolysis reactor, is at a temperature below 300°C, preferably below 250°C, more preferably below 200°C, and / or above the boiling point of the monomer and / or above 100°C.

4. 4. The process according to any one of claims 1 to 3, wherein the syrup is fed to the pyrolysis reactor (4), preferably in the vicinity of the inlet of the pyrolysis reactor (4), in particular in an intermediate section of the pyrolysis reactor (4) closer to the inlet than to the outlet.

5. 5. The process according to claim 4, wherein the intermediate section in which the syrup is fed to the pyrolysis reactor (4) is at a temperature below 450°C, preferably below 350°C, more preferably below 300°C, even more preferably below 250°C.

6. 6. The process according to any one of claims 1 to 5, wherein a solid polymer is injected into the pyrolysis reactor (4) to create a solid plug between the injection point of the syrup and the inlet of the pyrolysis reactor (4).

7. 7. The process according to any one of claims 1 to 6, wherein the temperature in the intermediate section of the pyrolysis reactor (4), located between the injection point of the syrup and the injection points of the solid and liquid impurities, is above 250°C, preferably above 350°C, in particular above 400°C.

8. The pyrolysis reactor (4) is a heated screw extruder comprising an elongated barrel (8) defined by a series of barrel sections (40) connected in series, and at least one screw (10) extending within the barrel (8) for conveying a feed material along the barrel (8); Each barrel section (40) is provided with a respective heating device (42) for heating the section of the barrel (8) corresponding to that barrel section (40); the inlet is located in a first barrel section (40) of the series of barrel sections (40); 8. The method of any one of claims 1 to 7, which is a heated screw extruder, the outlet of which is located in the last barrel section (40) of a series of barrel sections (40).

9. 9. The method of claim 8, wherein the solid impurities and liquid impurities are fed to the third to last barrel, the second to last barrel, and / or the last barrel section (40).

10. 10. The method of any one of claims 1 to 9, comprising separating solid and / or liquid impurities from the gas stream in a separation unit (14) before feeding the gas stream to the condenser (6).

11. scrubbing the gas stream between the separation unit (14) and the condenser (6) using a gas scrubbing unit (20) fluidly connected in series between the separation unit (14) and the condenser (6), the gas scrubbing unit comprises a transfer column (22) including internal components; 12. The method of claim 11, further comprising the step of: feeding the gas scrubbing unit with cold monomer in a liquid state, so that the gas stream flows upward in the transfer column (22), the cold monomer flows downward in the transfer column (22) by gravity, and heavy contaminants contained in the gas stream condense in a liquid state on the internal parts and flow down by gravity towards the bottom of the transfer column (22), and then being transferred to the separation unit (14).

12. 12. The process according to claim 11, wherein the cold monomer injected into the transfer column (22) is a fraction of the monomer solution recovered from the outlet of the condenser (6).

13. 13. The method of any one of claims 1 to 12, wherein the separation unit (14) comprises a main separator (16) and an auxiliary separator (18) fluidly connected in series.

14. 14. The method of any one of claims 1 to 13, wherein the monomer is methyl methacrylate (MMA) and the polymer is poly(methyl methacrylate) (PMMA).

15. 1. An installation for producing a monomer from a feed containing a polymer having the monomer as a component, comprising: A pyrolysis reactor (4) and a condenser (6), 15. An installation configured to carry out the manufacturing method according to any one of claims 1 to 14.

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