Patent Description:
The invention relates to the field of depolymerization for recovering a monomer from a feed material containing a polymer from which the monomer is a constituent.

In particular, the invention relates to the field of depolymerization of polymethyl methacrylate (PMMA) for recovering methyl methacrylate (MMA).

Recycled MMA is obtained for example by pyrolyzing solid PMMA wastes in a pyrolysis reactor, in particular a pyrolysis reactor provided as a heated screw extruder, such as to obtain a gas stream including gaseous MMA, removing unavoidable solid and/or liquid impurities included in the gas stream and condensing the gas stream to obtain liquid MMA.

The liquid MMA obtained from depolymerization of the PMMA is sometimes named "crude MMA".

Besides, some PMMA wastes are liquid products. These are typically syrups which are produced to make cast PMMA sheets and which cannot be used, for example because of quality defaults or change of product demands or failure of equipment, and which evolved too much during storage to guarantee proper product quality if used.

In view of improving the recycling efficiency, it would be advantageous to be able to process the solid and/or liquid impurities removed from the gas stream and/or liquid PMMA wastes.

<CIT> discloses a method of producing MMA. <CIT> and <CIT> disclose methods of recovering a monomer from a polymer. <NPL>, discloses experiments on pyrolyzing PMMA.

One of the aims of the invention is to propose a process of producing a monomer that allows obtaining a monomer solution with a satisfactory purity.

To the end, the invention proposes a method for the production of a monomer as defined in claim <NUM>.

A syrup means a solution of polymer and/or oligomers in the monomer, e.g. a solution of PMMA or MMA oligomers in MMA. Such syrup is obtained for example by a prepolymerization of the monomer, e.g. prepolymerization of MMA, as commonly done for the production of cast PMMA sheets. Alternatively, such a syrup is obtained for example by dissolution of the polymer in the monomer, e.g. the dissolution of PMMA in MMA. In the latter case it is preferable to use lower molecular weight polymer grades, e.g. lower molecular weight PMMA grades which might have a better solubility.

Solid and liquid impurities separated from the gas stream generated in the pyrolysis reactor may include depolymerization residues mixed with some monomer, e.g. MMA. The solid impurities include for example fine dusts of pigments and their degradation products, contaminating polymers, reinforcing agents such as glass and carbon fibers, wood residues, monomers and oligomers from other polymers as well as their degradation products when they are non soluble in the liquid medium. The liquid impurities may include the monomer, its oligomers, but also the polymer fraction which is soluble in the monomer, all the degradation products from the polymer itself and its contaminants. To some extent, the liquid impurities may comprise some water, hydrocarbons such as for example degradation products from the polyethylene film that covers PMMA sheets, aromatics such as toluene, xylenes and heavy aromatics generated by degradation of the polymers and contaminants but also generated from the decomposition of additives such as shock resistant additives. In practice, a major part of the liquid and solid impurities are constituted of the monomer, dimers and trimers and degradation products, but also combination of monomer and comonomers and their degradation products, as well as solutions of polymers and oligomers.

Optional features of the production method are defined in claims <NUM> - <NUM>.

The invention also relates to an installation for the production of a monomer as defined in claim <NUM>.

The invention and its advantages will be better understood upon reading the following description that is given solely by way of non-limiting example and given with reference to the appended drawings, in which:.

The depolymerization installation <NUM> of <FIG> is configured for the production of a monomer from a feed material F containing a polymer from which the monomer is a constituent.

The depolymerization installation <NUM> comprises a pyrolysis reactor <NUM> configured to receive the feed material and to generate a gas stream G containing the monomer in gaseous state and a condenser <NUM> configured for condensing the gas stream G such as to obtain a monomer solution M containing the monomer in liquid state.

In the following, the monomer solution M resulting from the condensing of the gas stream G is also referred to as the "crude monomer solution" or "crude monomer" or "liquid monomer".

The pyrolysis reactor <NUM> is advantageously a heated screw extruder comprising a heated barrel <NUM> and at least one screw <NUM> arranged inside the barrel <NUM> for moving the feed material through the barrel <NUM> with heating the feed material.

The depolymerization installation <NUM> comprises preferably a feeder <NUM> configured for feeding the feed material F to an inlet 4A of the pyrolysis reactor <NUM>.

The depolymerization installation <NUM> comprises optionally a separation unit <NUM> fluidly connected in series between an outlet 4B of the pyrolysis reactor <NUM> providing the gas stream G and the inlet of the condenser <NUM>, the separation unit <NUM> being configured for separating solid and/or liquid impurities from the gas stream G before feeding the gas stream G to the condenser <NUM>.

The separation unit <NUM> comprises for example a main separator <NUM> configured for diminishing the linear velocity of the gas stream G to promote the separation and deposit of solid impurities and/or for demisting the gas stream G to promote the deposition of mist droplets of liquid impurities and/or for washing the gas stream with a washing liquid to promote deposition of liquid impurities.

The diminution of the linear velocity of the gas stream G is obtained for example by a progressive increasing of the area of the cross-section of an internal flow passage of the main separator <NUM> through which the gas stream G passes in the main separator <NUM>.

Preferably, the main separator <NUM> is configured such that the internal flow passage of the main separator <NUM> does not follow a straight line. Such a configuration promotes separation and deposition of impurities.

The demisting of the gas stream G is obtained e.g. by providing one or several demisting grids across the internal flow passage of the main separator <NUM>.

The washing of the gas stream G is obtained e.g. by injection of water and/or injection of liquid monomer inside the internal flow passage of the main separator <NUM>.

The separation unit <NUM> comprises optionally an auxiliary separator <NUM> arranged upstream the main separator <NUM>. The gas stream G generated by the pyrolysis reactor <NUM> flows through the auxiliary separator <NUM> before entering the main separator <NUM>.

The auxiliary separator <NUM> is for example configured for removing solid impurities from the hot gas stream G by inertia.

The auxiliary separator <NUM> is for example configured with an internal flow passage having a change of cross section promoting a decrease of linear velocity and/or a change of direction that are located above a collecting pot such that the solid particles slowed down by the decrease of linear velocity and/or driven by inertia tend to hit walls of the internal flow passage and to fall down in the collecting pot.

Advantageously, the depolymerization installation <NUM> comprises a gas cleaning unit <NUM> connected in series between the separation unit <NUM> and the condenser <NUM> and configured for removing heavies from the gas stream G before the gas stream enters the condenser <NUM>.

The gas cleaning unit <NUM> is arranged such that the gas stream G exiting the separation unit <NUM> passes via the gas cleaning unit <NUM> before entering the condenser <NUM>.

The gas cleaning unit <NUM> comprises a transfer column <NUM> extending upwardly between a lower end 22A and an upper end 22B. The lower end 22A is fluidly connected to the separation unit <NUM>, in particular to the main separator <NUM>, for receiving the gas stream G exiting the separation unit <NUM>. The upper end 22B is fluidly connected to an inlet 6A of the condenser <NUM>.

The gas cleaning unit <NUM> comprises a reinjection loop <NUM> configured for reinjecting a fraction of the monomer solution collected at an outlet 6B of the condenser <NUM> into a top portion of the transfer column <NUM>, in particular at the top end 22B of the transfer column <NUM>.

The transfer column <NUM> is provided with internals. The internals comprise for example baffles, structure packing, gauze packing and/or random packing, e.g. random packing including saddles and/or rings, in particular Pall rings.

The internals are configured such that, in operation, the gas stream flows upwardly in the transfer column <NUM>, the temperature of the gas stream diminishing along the transfer column <NUM>, and the monomer solution injected in the transfer column <NUM> flows downwardly inside the transfer column <NUM> by gravity, heavy contaminants H contained in the gas stream condense on the internals and flow back in liquid state down the transfer column <NUM> and into the separation unit <NUM>, in particular into the main separator <NUM>.

The depolymerization installation <NUM> optionally comprises a purification unit <NUM> configured for purifying the monomer solution such as to obtain a purified monomer solution M containing less impurities.

The purification unit <NUM> comprises for example an evaporation-condensation unit configured for successively evaporating and condensing the monomer solution with removing heavies in the evaporator, one or several distillation columns, a thin-film evaporator, a short-path distillation unit and/or a crystallization unit comprising one or several crystallizers configured for performing a fractional crystallization, or any other appropriate technology or combination of technologies for purifying the monomer solution.

The installation <NUM> is configured for feeding the pyrolysis reactor <NUM> with solid and/or liquid impurities R separated from the gas stream G generated in the depolymerization installation <NUM> and/or from a gas stream generated in another depolymerization installation and/or with a syrup S containing the polymer and/or the monomer and/or oligomers of the monomer.

The depolymerization installation <NUM> comprises for example a reinjection line <NUM> configured for feeding the pyrolysis reactor <NUM> with solid and/or liquid impurities R separated from the gas stream generated in the depolymerization installation <NUM> and/or from a gas stream generated in another depolymerization installation.

For example, the reinjection line <NUM> connects the separation unit <NUM> to the pyrolysis reactor <NUM> for injecting solid and/or liquid impurities R separated from the gas stream G in the separation unit <NUM> into the pyrolysis reactor <NUM> and/or connects another separation unit <NUM> of another depolymerization installation to the pyrolysis reactor <NUM> for injecting solid and/or liquid impurities separated from the gas stream in this other separation unit <NUM> into the pyrolysis reactor <NUM>.

In particular, the reinjection line <NUM> connects the main separator <NUM> of the separation unit <NUM> to the pyrolysis reactor <NUM> and/or connects a main separator of the other separation unit <NUM> to the pyrolysis reactor <NUM>.

The depolymerization installation <NUM> comprises for example an injection line <NUM> configured for feeding the pyrolysis reactor <NUM> with the syrup S, for example from a syrup source <NUM>, such as a syrup reservoir.

The barrel <NUM> is preferably configured for heating the material contained in the barrel <NUM> according to a temperature profile, i.e. a temperature that varies along the barrel <NUM>.

Preferably, the pyrolysis reactor <NUM> is configured to generate a temperature profile that progressively increases and then progressively decreases from the inlet of the pyrolysis reactor <NUM> receiving the feed material to the outlet of the pyrolysis reactor <NUM> delivering the gas stream.

Typically, the temperature profile is such that an inlet temperature is higher than <NUM>, a maximum temperature is higher than <NUM>, in particular higher than <NUM>, more in particular higher than <NUM>, and an outlet temperature is higher than <NUM>.

Preferably, the solid and liquid impurities are fed to the pyrolysis reactor <NUM> in a section of the pyrolysis reactor <NUM> that is preferably proximate the outlet 4B of the pyrolysis reactor <NUM>, and in particular closer to the outlet 4B than the inlet 4A, i.e. the second half of the length of the barrel <NUM> of the pyrolysis reactor <NUM>.

The section of the pyrolysis reactor <NUM> in which the solid and liquid impurities R are fed to the pyrolysis reactor <NUM> is preferably at a temperature below <NUM>, preferably below <NUM>, still preferably below <NUM>.

The section of the pyrolysis reactor <NUM> in which the solid and liquid impurities R are fed to the pyrolysis reactor <NUM> is preferably at a temperature above <NUM> or a temperature above the boiling temperature of the monomer.

Preferably the syrup is fed to a section of the pyrolysis reactor <NUM> that is proximate the inlet 4A of the pyrolysis reactor <NUM>, and in particular closer to the inlet 4A than the outlet 4B, i.e. in the first half of the length of the barrel <NUM> of the pyrolysis reactor <NUM>.

The section of the pyrolysis reactor <NUM> in which the syrup S is fed to the pyrolysis reactor <NUM> is preferably at the temperature below <NUM>, more preferably below <NUM>, more preferably below <NUM>, preferably below <NUM>.

When both solid and/or liquid impurities R and syrup S are injected into the pyrolysis reactor <NUM>, they are preferably injected in separate sections of the pyrolysis reactor <NUM>. The point of injection of the solid and/or liquid impurities R into the pyrolysis reactor <NUM> is separate and distinct from the point of injection of the syrup S into the pyrolysis reactor <NUM>.

Preferably, feed material is injected in the pyrolysis reactor <NUM> such as to create a solid plug between the point of injection of the syrup S into the pyrolysis reactor <NUM> and the inlet 4A of the pyrolysis reactor <NUM> receiving the feed material F. In particular, the feed material F comprises or consists in solid material.

The presence of a plug in the pyrolysis reactor <NUM> prevents gaseous MMA and other decomposition products, solid and/or liquid impurities and/or syrup to flow backwards in the pyrolysis reactor <NUM>, towards the inlet 4A receiving the feed material F.

Preferably, the pyrolysis reactor <NUM> is configured such that the temperature in a section of the pyrolysis reactor <NUM> located between a point of injection of the syrup S and the point of injection of solid and/or liquid impurities R is above <NUM>, preferably above <NUM>, in particular above <NUM>.

As illustrated on <FIG>, the barrel <NUM> of the pyrolysis reactor <NUM> is for example defined by a series of barrel sections <NUM> (also called "barrel cylinders") connected in series, each barrel section <NUM> being provided with a respective heating device <NUM> for heating this particular barrel section <NUM>. Each barrel section <NUM> (or barrel cylinder) defines a portion of length of the barrel <NUM>.

The pyrolysis reactor <NUM> comprises for example an electrical control unit <NUM> configured for controlling the heating devices <NUM> of the barrel sections <NUM> individually such as to generate the desired temperature profile in the barrel <NUM>.

Preferably, the inlet of the pyrolysis reactor <NUM> receiving the feed material is located on the first barrel section <NUM> of the series of barrel sections <NUM> and/or the outlet of the pyrolysis reactor <NUM> delivering the gas stream G is located on the ultimate barrel section <NUM> of the series of barrel sections <NUM>.

Preferably, solid and/or liquid impurities R are fed in the antepenultimate barrel section <NUM>, the penultimate barrel section <NUM> and/or the ultimate barrel section <NUM> of the series of barrel sections <NUM>.

As illustrated on <FIG>, solid and/or liquid impurities R are fed in the penultimate barrel section <NUM> of the series of barrel sections <NUM>.

As illustrated on <FIG>, the syrup is fed in the second barrel section <NUM> of the series of barrel sections <NUM>.

This is illustrative only. In practice, the barrel section <NUM> in which the syrup is injected is chosen as a function of the operative conditions.

The syrup is 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.

In operation, the depolymerization installation <NUM> is configured for implementing a depolymerization method comprising the steps of:.

The production method further comprises feeding the pyrolysis reactor <NUM> with solid and/or liquid impurities R separated from the gas stream G generated in the depolymerization installation <NUM> and/or a gas stream generated in another depolymerization installation and/or with a syrup S containing the polymer and/or the monomer and/or oligomers of the monomer.

When applicable, the solid and/or liquid impurities R are preferably fed to the pyrolysis reactor <NUM> in a section of the pyrolysis reactor <NUM> that is proximate the outlet 4B of the pyrolysis reactor <NUM>, and in particular closer to the outlet 4B than the inlet 4A.

The section of the pyrolysis reactor <NUM> in which the solid and liquid impurities R are fed to the pyrolysis reactor <NUM> is preferably at a temperature above the boiling temperature of the monomer and/or a temperature above <NUM>.

When applicable, the syrup S is preferably fed to a section of the pyrolysis reactor <NUM> that is proximate the inlet 4A of the pyrolysis reactor <NUM>, and in particular closer to the inlet 4A than the outlet 4B.

The section of the pyrolysis reactor <NUM> in which the syrup S is fed to the pyrolysis reactor <NUM> is at the temperature below <NUM>, more preferably below <NUM>, more preferably below <NUM>, preferably below <NUM>.

Preferably, the depolymerization method comprises creating a solid plug between the point of injection of the syrup S into the pyrolysis reactor <NUM> and the inlet 4A of the pyrolysis reactor <NUM> receiving the feed material F.

The feed material F is preferably fed to the first barrel section <NUM> of a series of barrel sections <NUM> forming the barrel <NUM>.

The syrup S is for example fed in a barrel section comprised between the second barrel section <NUM> and the sixth barrel section <NUM> of the series of barrel sections <NUM>.

Preferably, the temperature of the gas stream G at the outlet of the main separator <NUM> and entrance of the transfer column <NUM> is maintained at least at the boiling point of the monomer, in particular at least at the boiling point of the monomer + <NUM>, in particular at least at the boiling point of the monomer + <NUM>, in particular at least at the boiling point of the monomer + <NUM>, more in particular at least at the boiling point of the monomer + <NUM>, even more in particular at least at the boiling point of the monomer + <NUM>.

Preferably the gas stream G at the outlet of the transfer column <NUM> is maintained between the boiling point of the monomer and the boiling point of the monomer + <NUM>, in particular between the boiling point of the monomer and the boiling point of the monomer + <NUM>, in particular between the boiling point of the monomer and the boiling point of the monomer + <NUM>, in particular between the boiling point of the monomer and the boiling point of the monomer + <NUM>, in particular between the boiling point of the monomer and the boiling point of the monomer + <NUM>.

The monomer if for example methyl methacrylate (MMA), the polymer being poly (methyl methacrylate) (PMMA).

The provision of the separation step performed in the separation unit <NUM> and the cleaning step performed in the cleaning unit <NUM> allows improving the quality of the monomer solution that is obtained.

Solid and/or liquid impurities R separated from a gas stream G generated by the pyrolysis reactor <NUM> of the depolymerization installation <NUM> or the pyrolysis reactor of another depolymerization installation generally contain various molecules, including the monomer (e.g. MMA), oligomers, additives, degradation products, solid residues from the polymer (e.g. PMMA) and other polymers that contaminated the polymer contained in the feed material, also termination by-products.

Returning solid and/or liquid impurities R including the monomer to the pyrolysis reactor <NUM> allows increasing the yield by recovering the monomer and depolymerized polymer contained in the solid and/or liquid impurities R separated from a gas stream G.

In particular, returning the solid and/or liquid impurities R in a section of the pyrolysis reactor <NUM> with a limited temperature, in particular a temperature below <NUM>, preferably below <NUM>, preferably below <NUM> appeared more appropriate.

Syrups S are difficult to recycle and the injection of the syrup S in the pyrolysis reactor <NUM> allows recycling syrups. The syrup S is more efficiently recycled with injection of the syrup in an upstream section of the pyrolysis reactor <NUM> such that the syrup is subjected to the temperature profile, in particular to the progressively increasing then progressively decreasing temperature.

Unexpectedly, it is possible to depolymerize more feed material when syrup is fed in the pyrolysis reactor <NUM> than when only feed material is depolymerized.

For a same amount of energy consumed in the pyrolysis reactor <NUM>, a higher total mass flow can be processed when syrup is fed in the pyrolysis reactor <NUM> in addition to the feed material.

The pyrolysis reactor <NUM> provided as a heated screw extruder uses mechanical and thermal energy for depolymerizing the polymer.

When injecting the syrup S in the pyrolysis reactor <NUM>, it is expected that the mechanical energy need is reduced.

Unexpectedly, the mechanical energy need remains stable. However, a lot of mechanical energy is provided in the first barrel sections <NUM> of the barrel <NUM> and once the polymer is melted, less mechanical energy is needed and more thermal energy is needed.

Hence, the point of injection of the syrup S shall be properly chosen so that, at point of injection of the syrup S, the feed material F is already melted and that the viscosity of the molten polymer has been sufficiently reduced so that most of the mechanical energy has been consumed.

In practice, depending on the length of the barrel <NUM> and the number of barrels sections <NUM>, this often corresponds to barrels sections <NUM> comprised between the second barrel section <NUM> and the sixth barrel section <NUM> of the series of barrels <NUM> of the barrel <NUM>.

In the production method, the injection of each the solid and/or liquid impurities and the syrup in the pyrolysis reactor <NUM> is for example operated continuously, at a constant rate or a varying rate, or intermittently, e.g. with injection phases alternating with non-injection phases. Varying rate and/or intermittent injection allow working with higher rates during high rate phase or injection phases, which may be easier to operate.

Examples <NUM> to <NUM> were implemented with injection of a syrup into the pyrolysis reactor <NUM>.

Examples <NUM> to <NUM> were implemented in a depolymerization installation <NUM> comprising the pyrolysis reactor <NUM>, a condenser <NUM>, a feeder <NUM>, a separation unit <NUM> and a gas cleaning unit <NUM>.

The pyrolysis reactor <NUM> was provided as a twin-screw extruder comprising a barrel <NUM> and two parallel screws <NUM> with co-rotation of the screws <NUM> and intermeshing of the screws <NUM>. The barrel <NUM> was made of a series of barrel sections <NUM>. Heaters <NUM> were provided for generating a temperature profile along the barrel <NUM>, the temperature profile progressively increasing and then decreasing along the barrel <NUM>, with a maximum profile temperature at an intermediate section of the barrel <NUM>.

More specifically, the twin-screw extruder was a TEX44 having a <NUM> screw diameter. For industrial production line, a TEX90 having a <NUM> screw diameter may be used according to the requested feeding rate. TEX extruders are marketed by The Japan Steel Works, Ltd which also offers larger units.

In operation, the pyrolysis reactor <NUM> had, along the length of the barrel <NUM>, a melting section followed by a depolymerization section. The feed material F was melted in the melting zone of the pyrolysis reactor <NUM> by shear stress from screws <NUM> and heat from the heaters <NUM>, then the melted material was transported to the depolymerization section. The depolymerization section of the pyrolysis reactor <NUM> could reach a temperature of <NUM>.

The condenser <NUM> was provided as a tube and shell heat exchanger.

The feeder <NUM> was as a gravimetric screw feeder <NUM>.

The separation unit <NUM> consisted in a main separator <NUM>. The separation unit <NUM> was not provided with an auxiliary separator <NUM> located upstream the main separator <NUM>.

The transfer between the separation unit <NUM> and the condenser <NUM> was performed via a transfer column <NUM> having a inner diameter of <NUM> and an internal provided as filter mesh. The filter mesh was a cylindrical grid with holes having a diameter of <NUM>. The filter mesh was inserted at an angle in the transfer column <NUM> so that the gas stream G was filtered through the filter mesh. The filter mesh was placed in the upper part of the transfer column <NUM>, closer to the condenser <NUM> than to the separation unit <NUM>.

The filter mesh was operated "dry", i.e. without monomer solution being reinjected in the transfer column.

The pyrolysis reactor <NUM> was configured with a barrel <NUM> made of a series of seventeen barrel sections named barrel section #<NUM> to barrel section #<NUM> in the following and equipped with an injection port of injection the MMA syrup located at the barrel section #<NUM>.

The table <NUM> below indicates the configuration of the pyrolysis reactor <NUM>, and in particular the function of each barrel section <NUM> and the set temperature of each barrel section <NUM> during the implementation of examples <NUM>, <NUM>, <NUM>:.

The barrel sections #<NUM> and #<NUM> are set at <NUM>, but with the heat transfer from the previous barrel section and hot gas, the actual temperature is usually higher.

The feed material used was cast clear PMMA sheets crushed into particles with a size of about <NUM> to <NUM>.

The syrup was a PMMA syrup containing a white pigment. The syrup was produced several days in advance and was a remaining from a cast sheet production. The syrup had an acceptable viscosity to be pumped into the pyrolysis reactor <NUM>. The syrup was stored in a tank at room temperature and under a controlled atmosphere. The syrup was pumped from the tank to the pyrolysis reactor <NUM> using a dosing pump that could feed up to <NUM>/h.

The feed material was depolymerized at <NUM> in the pyrolysis reactor <NUM> with a feed rate increased from <NUM> to <NUM>/h, and after <NUM> minutes of operation at <NUM>/h, a first sample of MMA solution was collected (Example 1a).

Then, the feeding rate was reduced to <NUM>/h, and after <NUM> minutes stabilization a second sample of MMA solution was collected (Example 1b).

Then, the feed rate was reduced to <NUM>/h, and the syrup injection was started at <NUM>/h in the fifth barrel section (barrel section #<NUM>). No significant variation in the screw temperature profile was recorded. After stabilization, a sample of MMA solution was collected (Example <NUM>).

After <NUM> minutes operation, the feed rate was kept at <NUM>/h and the syrup injection was increased to <NUM>/h, and, after stabilization, a new sample of MMA solution was collected. (Example <NUM>).

During the implementation of examples <NUM> and <NUM>, the temperature in barrel section #<NUM> was of respectively <NUM> and <NUM>. During the implementation of example <NUM>, the temperature in barrel section #<NUM> decreased to <NUM> in example <NUM>. Besides, the temperatures of the barrel sections #<NUM> and #<NUM> were affected by less than <NUM>, which is not significant, and the temperature of the barrel section #<NUM> was not affected.

The samples collected in examples 1a, 1b, <NUM> and <NUM> were analyzed by gas chromatography analysis to determine the MMA content of the MMA solution and some key impurities content.

As can be seen in the Table <NUM> below showing the results of the analysis, the MMA content remained around <NUM> to <NUM> wt%. Methanol and methyl isobutyrate content remained in the same range. Methyl acrylate and ethyl acrylate were comonomers present in the Cast PMMA used as feed material. Their content decreased as the PMMA scraps were partly substituted by the syrup which did not contain those comonomers. The reduction in ethyl acrylate from example 1a and 1b to example <NUM> and <NUM> follow a linear correlation and is not due to an artifact.

The amount of heavies in the MMA solution (or "crude MMA") was estimated by the gas chromatography analysis of products having a much higher retention times than the MMA. When substituting part of the PMMA scraps (feed material) by the MMA syrup the amount of heavies determined as gas chromatography peaks area percentage of the products detected, was reduced slightly.

These examples show that it was possible to substitute a significant amount of PMMA scraps with MMA syrup without affecting negatively the crude MMA quality. The heavies did not increase in this case, showing that the MMA oligomers which are present in the syrup did not affect the crude MMA purity.

The productivity of the depolymerization installation is increased. With PMMA scraps only, the maximum productivity of the depolymerization installation was limited to <NUM>/h in the same conditions. But when replacing <NUM>/h of PMMA scraps by MMA syrup, it was possible to feed <NUM>/h of syrup while keeping the performance of the depolymerization installation.

Examples <NUM>, <NUM>, <NUM> with the pyrolysis reactor <NUM> configured with the syrup injection port located respectively in barrel sections #<NUM>, #<NUM> and #<NUM> instead of barrel #<NUM> may be contemplated.

For such examples <NUM>, <NUM>, <NUM>, the amount of syrup which would be injected limited by the visual detection of a non-depolymerized fraction at the outlet 4B of the pyrolysis reactor <NUM> or in the separation unit <NUM>. The MMA syrup feeding rate would then be adjusted to the maximum amount, and then the depolymerization installation would be stabilized for data acquisition.

Table <NUM> below shows expected results for examples <NUM> to <NUM>.

According to these expected results of table <NUM>, the productivity of the depolymerization installation is reduced when the MMA syrup is injected in the downstream half of the barrel <NUM> and the maximum amount MMA syrup which can be injected in the pyrolysis reactor <NUM> is limited.

It is supposed that it is preferable to inject the syrup in an upstream section of the barrel <NUM> of the pyrolysis reactor <NUM>, in particular in a section upstream the section(s) at the maximum profile temperature.

Examples <NUM> to <NUM> may be implemented notable with providing a gas cleaning unit <NUM> and with reinjecting liquid heavies collected in the main separator <NUM> to the pyrolysis reactor <NUM>. The depolymerization installation <NUM> would thus be modified as follows:.

The following adjustable parameters are expected to have impact the quality of the crude MMA and the yield of the depolymerization:.

For examples <NUM>, <NUM> and <NUM>, the feed material would be an injection grade PMMA product, from car tail lights collected at a deconstruction site treating end-of-life vehicles, crushed to small particles. These PMMA scraps generally have a mix of colors (red, black, transparent, orange. ) and are also contaminated by other polymers such as polycarbonate and ABS.

The PMMA scraps would be fed at a <NUM>/h rate in the pyrolysis reactor <NUM> operated with a maximum profile temperature of <NUM> and with a screw rotation speed of <NUM> rpm, with a back flow of crude MMA from the condenser <NUM> back to the gas cleaning unit <NUM> adjusted to about <NUM>/h.

The barrel <NUM> of the pyrolysis reactor <NUM> would be equipped with an injection port located at barrel section #<NUM> for injecting the liquid heavies collected from the separation unit <NUM>. The pyrolysis reactor <NUM> would thus be configured as indicated in table <NUM> below:.

Expected results are indicated in table <NUM> below.

For examples <NUM>, <NUM>, and <NUM>, the liquid injection port would be moved to respectively barrels section #<NUM>, #<NUM> and #<NUM>. The barrel section preceding the barrel section with the liquid injection would be cooled to <NUM>. The pyrolysis reactor <NUM> would be reconfigured for each example.

For example, the pyrolysis reactor <NUM> would configured as indicated in table <NUM> below for the example <NUM>:.

Claim 1:
A method for the production of a monomer from a feed material containing a polymer from which the monomer is a constituent, the production method being implemented in a depolymerization installation (<NUM>) comprising a pyrolysis reactor (<NUM>) and a condenser (<NUM>), the production method comprising the steps of:
- pyrolizing the feed material in the pyrolysis reactor (<NUM>) so as to generate a gas stream, the feed material travelling from an inlet of the pyrolysis reactor (<NUM>) to an outlet of the pyrolysis reactor (<NUM>) with being subjected to heat such as to generate the gas stream at the outlet of the pyrolysis reactor (<NUM>); and
- condensing the monomer contained in the gas stream in the condenser (<NUM>) such as to obtain liquid monomer;
the production method further comprising feeding the pyrolysis reactor (<NUM>) with solid and/or liquid impurities separated from the gas stream generated in the depolymerization installation (<NUM>) and/or a gas stream generated in another depolymerization installation and/or with a syrup containing the polymer and/or the monomer and/or oligomers of the monomer.