BE1031630A1 - PROCESS FOR THERMOMECHANICALLY DEVULCANIZING A VULCANIZED ELASTOMER - Google Patents

Abstract

A method for thermomechanically devulcanizing an elastomer, comprising the steps of providing a vulcanized elastomer in the form of particles, feeding said particles upstream of an extruder, which comprises at least one twin-screw comprising at least one reverse-pitch screw element, and which is arranged to move said particles within it, thermomechanical treatment of said particles and feeding said devulcanized material to an outlet to recover a devulcanized material.

Description

PROCESS FOR THERMOMECHANICALLY DEVULCANIZING AN ELASTOMER

VULCANIZED

The present invention relates to a method for thermomechanically devulcanizing a vulcanized elastomer and also to an extruder for thermomechanically devulcanizing a vulcanized elastomer.

Vulcanization is a process that allows the macromolecules of an elastomer to be linked together by adding a vulcanizing agent, such as sulfur, in order to give elastic properties to the treated material. This avoids permanent deformations, due to viscous flow. Typically, the vulcanization of natural rubber is carried out by heating a rubber to a certain temperature, after mastication and the addition of sulfur, plasticizers, zinc oxide and accelerators.

At the end of their life, these vulcanized products, such as truck and aircraft tires, are stored without any real recovery.

The storage of these used materials is becoming increasingly complicated to manage and generates relatively significant costs.

Recycling these used materials by recovering them in new products makes it possible to avoid these storages and ensures sustainable circularity in the elastomer industry, particularly in the world of rubber. The challenge lies in the quality of the recycled product which must meet specifications depending on the intended application. This would promote the use of recycled materials without skimping on the properties of the material supplied based on recycled material. Given the volumes available in end-of-life vulcanized elastomers, any recovery route would be welcome.

Generally, the recycling of vulcanized elastomers includes that of rubber, for example from used tires, which typically takes shape through devulcanization processes.

These break the sulfur bonds initially formed during vulcanization in order to give new life to the treated products.

Thus, there are different types of devulcanization. For example, a devulcanization that involves the use of chemicals to alter the product to be treated and break the sulfur bonds. In addition, this chemical treatment can be combined with a (thermo)mechanical treatment. A devulcanization can also be carried out by applying microwave waves or by ultrasound. Finally, there are also devulcanization processes that consist of applying a thermomechanical treatment.

US 2009 082 475 discloses a process for devulcanizing vulcanized rubber. The latter is mixed with chemical additives before being introduced into an extruder to carry out the devulcanization.

WO 2022 044 031 discloses another method for devulcanizing vulcanized rubber which is done thermomechanically and in the absence of chemical additives. The extruder provides a production rate of devulcanized material of between 2 and 10 kg/hour.

Unfortunately, current devulcanization processes do not allow easy, rapid and efficient devulcanization, especially on an industrial scale.

There is a need to significantly reduce the use of chemicals to achieve devulcanization, while maintaining effective devulcanization that meets current environmental needs, with an economically viable process. Furthermore, it would be advantageous to be able to apply a devulcanization process without changing the basic formula of the treated rubber (or very little).

The aim of the present invention is to provide a simple and effective method for devulcanizing a thermomechanically vulcanized elastomer which is energy efficient and simple to implement.

To solve this problem, the invention provides a method for thermomechanically devulcanizing a vulcanized elastomer, comprising the following steps: - Providing a vulcanized elastomer in the form of particles having a predetermined size distribution, - Providing an extruder which comprises at least one rotatably mounted twin-screw, preferably co-rotatably mounted, which extends in at least 3 sections of said extruder, a receiving section located upstream, a devulcanization section and an outlet section located downstream, - Feeding said particles upstream of said extruder which is arranged to move said particles within it following a rotational movement of said at least one twin-screw, downstream thereof, towards the outlet section, - Optionally, grinding said particles in a grinding section to reduce the particle size, - Thermomechanical treatment of said particles in the devulcanization section to form a material devulcanized,

- Feeding said devulcanized material to the outlet section to recover said ready-to-use devulcanized material, characterized in that said at least one twin-screw which extends into the devulcanization section is provided with at least one reverse-pitch screw element which is arranged to allow movement of the particles in the opposite direction, relative to the direction of movement of said particles fed upstream of said extruder, and to maintain them for a period of time sufficient to allow devulcanization and in that these particles fed in the opposite direction are thermomechanically treated after they have been in contact with said reverse-pitch screw element.

The method according to the invention makes it possible to devulcanize a vulcanized material, which is supplied in the form of particles (granules, powder, shavings, etc.) in an extruder which comprises at least one twin-screw mounted to rotate, preferably co-rotating or counter-rotating.

The devulcanization process according to the invention makes it possible to break at least the carbon-sulfur (C-S) and sulfur-sulfur (S-S) bonds of the treated particles.

The extruder has 3 sections: a reception section located upstream ready to receive the particles to be treated, a devulcanization section for thermomechanically treating these particles and an outlet section located downstream to ensure the outlet of the particles previously treated in the devulcanization section. Said at least one twin-screw extends in said at least 3 sections, preferably from said reception section to said outlet section.

Advantageously, said devulcanization section is located between said reception section and said outlet section.

When the particles are brought into the receiving section, they are moved by the rotation (for example by means of a motor) of said at least one twin-screw towards the devulcanization section. 5 Said at least one twin-screw extending into the devulcanization section comprises at least one screw element with a reverse pitch, relative to the direction of movement of said particles within said extruder provided upstream thereof. Indeed, the particles are moved from the receiving section towards the outlet section following the rotation of said at least one twin-screw. Thus, when the particles reach the devulcanization section, they are thermomechanically treated after having been in contact with said screw element with a reverse pitch.

More specifically, said at least one reverse-pitch screw element located in the devulcanization section slightly returns the particles upstream (backward relative to the direction of travel), which generates a certain pressure at said at least one reverse-pitch screw element and makes it possible to retain these particles in the devulcanization section. It is at this location that the devulcanization operates effectively and makes it possible to break the C-S and/or S-S bonds of the treated particles, preferably without the addition of chemical devulcanization agents. The temperature applied in the devulcanization section can thus be greater than 250 °C, preferably greater than 300 °C, more preferably still greater than 320 °C.

In operation (when the particles are continuously fed into the extruder), the particles that are fed into the extruder will exert pressure on the devulcanized material that has been pushed backwards (with respect to the direction of travel, i.e. from the receiving section to the outlet section) by the at least one reverse-pitch screw element, which leads to the passage of the devulcanized material towards the outlet section. A kind of looping movement is then established at this point (at the reverse-pitch screw element) in that the particles to be treated are first pushed backwards and after devulcanization, the material is moved towards the outlet section.

Thus, the method according to the invention allows the particles to move in the opposite direction and to be kept in the devulcanization section for a sufficient period of time to carry out the devulcanization, preferably between 0.1 and 10 seconds, more preferably between 1 and 6 seconds.

The duration of devulcanization can be between 1 and 4 seconds.

In a preferred embodiment, said particles are heated in the receiving or devulcanization section. The temperature is adjusted so as to reach a temperature sufficient to allow devulcanization.

It may be advantageous to carry out the devulcanization in a section of said extruder in an easy and efficient manner for the user by applying the desired temperature in the devulcanization section or by preparing the particles in the receiving section in order to better control the temperature in the devulcanization section (read without further temperature increase).

Preferably, the temperature applied in the devulcanization section can thus be greater than 210°C, preferably greater than 250°C, more preferably greater than 320°C.

Advantageously, said sufficient temperature applied at the level of the reverse pitch screw element is possibly the highest temperature applied compared to the temperatures prevailing in the other sections of said extruder. This has the advantage of targeting an adequate devulcanization temperature to properly treat the particles, while allowing efficient temperature management during extrusion.

Alternatively, it is also possible to apply a temperature in the receiving section that is higher than the temperatures applied in the other sections of the extruder. This can make it possible to bring the particles to a temperature suitable for devulcanization. Thus, when they reach the devulcanization section, the temperature is such that it is not necessary to further heat the particles which are ready to be devulcanized.

The reception section can thus serve as a pre-heating stage before carrying out devulcanization in the corresponding section.

According to an advantageous embodiment, the grinding section corresponds to the reception section in which the possible grinding of the particles is carried out. Advantageously, the reception section comprises a grinding section which constitutes a part thereof.

Even more advantageously, the devulcanized material is produced by means of the extruder at a throughput of maximum 500 kg/h, preferably maximum 350 kg/h, more preferably maximum 300 kg/h, more preferably maximum 250 kg/h, even more preferably maximum 200 kg/h, advantageously maximum 150 kg/h. This has the advantage of carrying out the devulcanization quickly and efficiently to process large quantities of vulcanized elastomer.

Preferably, the devulcanized material is produced by means of the extruder at a flow rate of at least 50 kg/h, preferably at least 100 kg/h.

The flow rate expressed above is a function of the size of the extruder which is defined in relation to the diameter of the barrel in which said at least one twin-screw is housed. The barrel has a diameter of between 55 and 65 mm, preferably between 60 and 65 mm. Advantageously, the barrel has a diameter of 60 mm OR 65 mm. The flow rate values given above correspond to a barrel with an (external) diameter of 65 mm.

Preferably, said at least one twin-screw which is located in the devulcanization section comprises at least 2 screw elements, a mixing screw element arranged to carry out the devulcanization followed by a reverse pitch screw element arranged to retain the particles and allow counter-movement.

Thus, the method according to the invention can advantageously be characterized in that said at least one twin-screw which extends into the devulcanization section is provided with at least one mixing screw element followed by the reverse-pitch screw element which is arranged to allow movement of the particles in the opposite direction, relative to the direction of movement of said particles brought upstream of said extruder, and a holding of the latter for a period of time sufficient to allow devulcanization and in that these particles brought in the opposite direction are treated thermomechanically by said mixing screw element, after they have been in contact with said reverse-pitch screw element.

Surprisingly, the combination of this mixing screw element and this reverse pitch screw element which constitutes the last screw element of the devulcanization section makes it possible to carry out the devulcanization efficiently without requiring a high heat input. Thus, the reverse pitch screw element which is located in the devulcanization section slightly returns the particles upstream (backwards relative to the direction of movement), which generates a certain pressure at the level of said at least one reverse pitch screw element and allows said particles to be held. Then, the mixing screw element will make it possible to carry out the devulcanization efficiently by breaking the C-S and/or S-S bonds of the treated particles, preferably without adding chemical devulcanization agents. Thanks to the combination of the masticating screw element and the reverse pitch screw element, the temperature applied in the devulcanization section can advantageously be 220 °C, preferably maximum 210 °C. This is particularly advantageous for the user who will be able to control the temperature within the extruder more easily, reducing the risk of material damage.

In operation (when the particles are continuously fed into the extruder), the particles that are fed into the extruder will thus exert pressure on the devulcanized material, which leads to the passage of the devulcanized material towards the outlet section. A sort of loop movement is then established at this point (at the level of the reverse pitch screw element and the mixing screw element) in that the particles to be treated are first pushed backwards and held and then moved towards the outlet section. Thus, the reverse pitch screw element retains the particles for the duration of the devulcanization which is carried out by the mixing screw element.

Advantageously, the reverse pitch screw element constitutes the last screw element of the devulcanization section.

Even more preferably, said at least one twin-screw which is located in the devulcanization section has at least one mixing screw followed by the reverse pitch screw element, which constitutes the last screw element in the devulcanization section, before passing into the outlet section.

In an even more advantageous embodiment, said at least one twin-screw of the extruder has a rotation speed of between 50-600 rpm (rotation per minute), preferably between 250 and 450 rpm, preferably between 300 and 400 rpm. This has the advantage of carrying out the devulcanization quickly and efficiently.

These rotation speeds depend on the quantity of material processed (example: 60 rpm for 10 kg/h, 120 rpm to process up to 80 kg/h, 200 rpm to process up to 150 kg/h, 250 rpm to process up to 200 kg/h, 300 rpm to process up to 250 kg/h....).

According to an exemplary embodiment according to the invention, said particles move in the opposite direction by the effect of the reverse-pitch screw element and are thus retained in the devulcanization section for a period of between 0.1 and 10 seconds, preferably between 1 and 6 seconds. This has the advantage of allowing rapid and efficient devulcanization.

According to a preferred example, said particles present in the devulcanization section have a residence time of between 1 and 4 seconds. This has the advantage of carrying out the devulcanization quickly and efficiently.

Advantageously, the reception and devulcanization sections are heated to allow conditioning of the particles before devulcanization.

Preferably, said devulcanization section corresponds to at least one module which has a length equal to approximately 4 times the diameter of said extruder.

In an advantageous embodiment, cooling of the devulcanized material is carried out in said outlet section, preferably to a temperature of between 20 and 100°C. This has the advantage of obtaining a stabilized devulcanized material which has

A viscosity between 20 and 120 Mooney, preferably between 40 and 70 Mooney, measured according to ISO-289 or ASTM D1646-19a.

According to a preferred embodiment, the temperature applied within said devulcanization section is between 180 and 250°C. This has the advantage of carrying out the devulcanization efficiently without degrading the C-C bonds within the particles. Also, the temperature applied depends on the type of elastomer particles treated.

According to an advantageous embodiment, said devulcanization section has a length of between 4 and 8 times the diameter of the extruder, preferably between 4 and 6 times the diameter of the extruder, more preferably equal to 4 times the diameter of the extruder. This has the advantage of carrying out the devulcanization in a well-defined section of the extruder.

In a preferred embodiment, the method according to the invention has an energy consumption less than or equal to 0.5 kWh/kg, preferably less than or equal to 0.4 kWh/kg.

Preferably, the method according to the invention is carried out continuously.

Thus and advantageously, the step of supplying said particles upstream of said extruder is operated continuously.

Other advantages and embodiments of the invention are set forth in the claims.

The present invention also relates to an extruder for thermomechanically devulcanizing a vulcanized elastomer,

comprising at least one rotatably mounted twin-screw, preferably co-rotatably mounted, which extends in at least 3 sections, a reception section located upstream, a devulcanization section and an outlet section located downstream, said extruder being arranged to move the vulcanized elastomer in the form of particles within it following a rotational movement of said at least one twin-screw downstream thereof, in the direction of the outlet section, characterized in that said at least one twin-screw which extends in the devulcanization section is provided with at least one reverse-pitch screw element which is arranged to allow a movement of the particles in the opposite direction, relative to the direction of movement of said particles brought upstream of said extruder, and a maintenance of the latter for a period of time sufficient to allow devulcanization and in that these particles brought in the opposite direction are treated thermomechanically after they have been in contact with said reverse-pitch screw element.

In a preferred embodiment, said particles are heated in the receiving or devulcanization section. The temperature is adjusted so as to reach a temperature sufficient to allow devulcanization.

It may be advantageous to carry out the devulcanization in a section of said extruder in an easy and efficient manner for the user by applying the desired temperature in the devulcanization section or by preparing the particles in the receiving section in order to better control the temperature in the devulcanization section (read without increasing the temperature subsequently).

Preferably, the temperature applied in the devulcanization section can thus be greater than 210°C, preferably greater than 250°C, more preferably greater than 320°C.

Advantageously, said sufficient temperature applied at the level of the reverse pitch screw element is possibly the highest temperature applied compared to the temperatures prevailing in the other sections of said extruder. This has the advantage of targeting an adequate devulcanization temperature to properly treat the particles, while allowing efficient temperature management during extrusion.

Alternatively, it is also possible to apply a temperature in the receiving section that is higher than the temperatures applied in the other sections of the extruder. This can make it possible to bring the particles to a temperature suitable for devulcanization. Thus, when they reach the devulcanization section, the temperature is such that it is not necessary to further heat the particles which are ready to be devulcanized.

The reception section can thus serve as a pre-heating stage before carrying out devulcanization in the corresponding section.

In one embodiment of the invention, the devulcanization section may have a maximum temperature when the particles come into contact with said reverse-pitch screw element. This has the advantage of performing devulcanization in a section of said extruder in an easy and efficient manner for the user.

In one embodiment, this maximum temperature at the reverse pitch screw element is also the highest temperature applied in the devulcanization section and also relative to the temperatures prevailing in the other sections of said extruder. This has the advantage of targeting an adequate temperature for devulcanization for the particles to be treated, while allowing efficient management thereof during extrusion.

In a preferred embodiment, the extruder delivers a devulcanized material at a flow rate of maximum 500 kg/h, preferably maximum 350 kg/h, more preferably maximum 300 kg/h, more preferably maximum 250 kg/h, more preferably still maximum 200 kg/h, advantageously maximum 150 kg/h. This has the advantage of carrying out the devulcanization quickly and efficiently to treat large quantities of vulcanized elastomer.

According to an advantageous embodiment, the reception section may comprise a particle grinding section.

Advantageously, the extruder delivers a devulcanized material at a flow rate of at least 50 kg/h, preferably at least 100 kg/h.

The flow rate expressed in the context of the present invention is a function of the size of the extruder which is defined relative to the diameter of the barrel in which said at least one twin-screw is housed. The barrel has a diameter of between 55 and 65 mm, preferably between 60 and 65 mm. Advantageously, the barrel has a diameter of 60 mm or 65 mm. The flow rate values given above correspond to a barrel with an (external) diameter of 65 mm.

In an even more advantageous embodiment, said at least one twin-screw which is located in the devulcanization section comprises at least 2 screw elements, a mixing screw element followed by a reverse-pitch screw element arranged to carry out the devulcanization. This has the advantage of preparing the particles for devulcanization by mixing and then allowing devulcanization thanks to the reverse-pitch screw element.

Preferably, the reverse pitch screw element constitutes the last screw element of the devulcanization section.

Even more preferably, said at least one twin-screw which is located in the devulcanization section has a series of mixing screws followed by the reverse pitch screw element, which constitutes the last screw element in the devulcanization section, before passing into the outlet section.

In an even more advantageous embodiment, said at least one twin-screw of the extruder has a rotation speed (expressed in rotations per minute) of between 50-600 rpm, preferably between 250 and 450 rpm, preferably between 300 and 400 rpm. This has the advantage of carrying out the devulcanization quickly and efficiently.

These rotation speeds depend on the quantity of material processed (example: 60 rpm for 10 kg/h, 120 rpm for processing up to 80 kg/h, 200 rpm for processing up to 150 kg/h, 250 rpm for processing up to 200 kg/h, 300 rpm for processing up to 250 kg/h....).

According to an exemplary embodiment according to the invention, said particles move in the opposite direction by the effect of the reverse-pitch screw element and are thus retained in the devulcanization section for a period of between 0.1 and 10 seconds, preferably between 1 and 6 seconds. This has the advantage of allowing rapid and efficient devulcanization.

According to a preferred example, said particles present in the devulcanization section have a residence time of between 1 and 4 seconds. This has the advantage of carrying out the devulcanization quickly and efficiently.

Advantageously, the reception and devulcanization sections are heated to allow conditioning of the particles before devulcanization.

Preferably, said devulcanization section corresponds to at least one module which has a length equal to approximately 4 times the diameter of said extruder.

Preferably, the outlet section has a temperature between 20 and 100 °C. This avoids having to place a cooling bath outside the extruder. Thus, the devulcanized material is easily extracted from the extruder.

In one embodiment, the temperature within said devulcanization section is between 180 and 250°C. This has the advantage of carrying out the devulcanization efficiently without degrading the C-C bonds within the particles.

Advantageously, said devulcanization section has a length of between 4 and 8 times the diameter of the extruder, preferably between 4 and 6, more preferably equal to 4. This has the advantage of carrying out the devulcanization in a well-defined section of the extruder.

Preferably, said at least one reverse-pitch screw element constitutes the last screw element of the devulcanization section which is preceded by a mixing screw element arranged to devulcanize the particles fed in the opposite direction and held by said at least one reverse-pitch screw element in order to be able to carry out the devulcanization.

According to one embodiment, the devulcanization section has a temperature of between 120 and 250°C, preferably between 120 and 220°C. According to an advantageous embodiment, the devulcanization takes place at a temperature not exceeding 210°C, in particular when the mixing screw element precedes the reverse pitch screw element present in the devulcanization section.

In a preferred embodiment, the method according to the invention has an energy consumption less than or equal to 0.5 kWh/kg, preferably less than or equal to 0.4 kWh/kg.

The method according to the present invention is advantageously carried out in the absence of chemical agents.

In the context of the present invention, the expression "free of chemical agents" means substantially free, in particular in an amount of less than 1% by weight, preferably less than 0.5% by weight relative to the total weight of elastomers to be treated.

The expression "extruder diameter" must be understood within the meaning of the present invention as corresponding to the (external) diameter of a barrel in which said at least one twin-screw is housed. The barrel may have a diameter of between 55 and 65 mm, preferably between 60 and 65 mm. Advantageously, the barrel has a diameter of 60 mm or 65 mm.

The expression "ready-to-use devulcanized material" means that the material supplied at the end of the process can be compounded with other compounds to allow vulcanization, the parameters of which will depend on the intended application.

Said vulcanized elastomer advantageously comes from a vulcanized elastomer waste selected from the group consisting of ethylene-propylene-diene monomer (EPDM), styrene-butadiene (SBR), natural rubber (NR), synthetic isoprene (IR) and their mixtures, preferably in the form of chips, granules or powders.

The particles according to the present invention can thus be chosen from the group comprising chips, granules, powder and their mixtures.

Said particles have a predetermined size distribution depending on the type of elastomer to be devulcanized, preferably less than 8 mm, more preferably less than 5 mm. The size distribution is a medium size distribution.

Furthermore, the person skilled in the art knows GTR tires (in English for ‘Ground Tire Rubber’) which comprise an elastomer selected from the group consisting of SBR, NR, SBR and their mixtures. This may constitute the starting material, read the vulcanized elastomer provided in the form of particles.

The extruder according to the invention mainly comprises at least one twin-screw mounted rotatably, preferably on an axis powered by a motor and comprises at least 3 sections, an inlet section, a devulcanization section and an outlet section. Said at least one twin-screw is composed of a series of screw elements which can have different profiles, depending on the function to be applied such as for example conveying, kneading, shearing, grinding, etc.

Also, said at least one twin-screw extends in said at least 3 sections of said exiruder (from the reception section to the devulcanization section and finally in the outlet section).

Preferably, each section of said extruder comprises a twin-screw. Thus, the extruder can comprise 3 twin-screws assembled together.

The extruder according to the invention may comprise a sheath in which said at least one twin-screw is housed. The sheath then extends from said inlet section to said outlet section via the devulcanization section.

The sheath according to the invention can be heated or cooled at each section independently in order to ensure a controlled temperature profile over the entire length of said at least one twin-screw.

Advantageously, each section of the extruder of the invention defines at least one module which corresponds to a cylindrical sheath through which said at least one twin-screw is located.

The ratio (L/D) corresponds to the length of the screw (L) and the diameter (D) of the extruder.

According to the invention, when the extruder comprises a twin-screw extending over said 3 sections, said twin-screw has an L/D ratio of between 16 and 256, preferably between 32 and 128, more preferably between 32 and 70, advantageously between 62 and 69, more advantageously equal to 64 or 68.

In addition, the inlet section corresponds to at least one module which has a length of between 10 and 40 times the diameter of the extruder, preferably between 10 and 30 times the diameter of the extruder, more preferably between 20 and 28 times the diameter of the extruder.

Preferably, the outlet section corresponds to a module which has a length of between 10 and 50 times the diameter of the extruder, preferably between 10 and 40 times the diameter of the extruder, more preferably between 20 and 38 times the diameter of the extruder.

Advantageously, the reception section includes

A grinding section which corresponds to at least one module having a length between 1 and 10 times the diameter of the extruder, preferably between 4 and 10 times the diameter of the extruder, more preferably still between 5 and 9 times the diameter of the extruder.

Said devulcanization section comprises at least 2 screw elements having different profiles.

The last screw element of said devulcanization section is a reverse pitch screw element.

Preferably, the extruder according to the present invention operates in a steady state.

In the context of the present invention, a permanent regime means that the extruder is implemented in such a way that the quantity of material entering corresponds to the quantity of material leaving the extruder. || There may thus be accelerations of the particles/materials and slowdowns but the overall balance corresponds to a permanent regime, known to the person skilled in the art.

The present invention relates to a method for thermomechanically devulcanizing a vulcanized elastomer.

The vulcanized elastomer is advantageously an elastomer from an end-of-life product such as tires, various rubber materials. These materials are treated to provide the particles according to the invention. The use of elastomer from an end-of-life product allows the process to be part of a recycling and circular economy logic, while giving the newly formed product the desired mechanical properties depending on the intended application.

The particles are fed into the receiving section of the extruder according to the invention. The extruder comprises at least one rotatably mounted twin-screw, preferably co-rotating, which extends into at least 3 sections of the extruder. Indeed, the extruder comprises at least said receiving section, the devulcanization section and the outlet section.

This is how the twin-screw extends over all of the said sections.

Preferably, the extruder is equipped with at least

A sheath which allows said at least one twin-screw to be housed. Said at least one twin-screw is formed of a series of screw elements which have profiles depending on the function to be performed and the section in which they are located.

Thus, the receiving section will preferably comprise mixing screw and/or conveying elements in order to move the particles towards the devulcanization section. Preferably, within the receiving section, the particles can be heated to a temperature of approximately 140°C.

The devulcanization section contains screw elements which will advantageously allow a mixing and at one of its ends (towards the outlet section) a thermomechanical devulcanization which will allow the particles to be devulcanized by means of the reverse pitch screw element. More advantageously, the devulcanization section comprises a mixing screw element followed by a reverse pitch screw element (last screw element of the devulcanization section).

Before accessing the devulcanization section, the reception section may allow grinding of the supplied particles so as to further improve/facilitate the devulcanization step. In this case, the reception section may then comprise grinding screw elements.

To do this, it is thus possible to have a succession of mixing screw elements to then reach at least one (preferably one) reverse pitch screw element as described in the context of the present invention. Advantageously, this screw element constitutes the last screw element present in the devulcanization section.

As explained, this is where the particles will be moved in a loop-like motion. More specifically, the possibly previously conveyed and/or kneaded particles will reach the reverse-pitch screw element where the pressure is such that the particles will be pushed backwards and held in place to allow thermomechanical devulcanization preferably carried out with at least one kneading screw element. Thus, the newly supplied particles (particles to be treated) in the receiving section will push the devulcanized material toward the outlet section. This can be illustrated by a loop of movement of the devulcanized material, pushed by the particles to be treated, toward the outlet section. This thermomechanical treatment allows the breaking of the C-S and S-S bonds of the particles (possibly crushed) to obtain the devulcanized material. The supply of the particles upstream of the extruder is preferably carried out continuously.

Counter-moving particles increases the residence time of the particles within the extruder.

The particles have a residence time of between 1 and 4 seconds in the devulcanization section, starting from the moment they are pushed back by said at least one reverse-pitch screw element and retained in the devulcanization section for the aforementioned residence time. When the residence time has elapsed, the devulcanized material is pushed towards the outlet section.

In this way, the devulcanized material reaches the outlet section where the temperature is such that it can be received outside the extruder as a ready-to-use devulcanized material.

Alternatively, it is also possible to provide a devulcanized material at the extruder outlet which has a high temperature which requires cooling outside the extruder. The person skilled in the art knows that a cooling bath can be provided at the extruder outlet to enable a ready-to-use devulcanized material to be provided.

Thus, the output section preferably comprises a series of conveying screw elements.

Preferably, the outlet section can allow cooling of the devulcanized material.

According to a preferred embodiment, the different sections of the extruder can be equipped with a cooling system throughout the extruder in order to manage the temperature according to the type of elastomer to be treated.

Each section can also correspond to a module in which these screw elements are present.

In the outlet section, the devulcanized material is cooled to a temperature of approximately 50°C.

The screw elements making up the outlet section have a screw profile allowing the mixing and movement of the devulcanized material in order to adjust the viscosity of the devulcanized material at the outlet of the extruder.

The output rate of the extruder is 300 kg/hour.

Example 1

The devulcanization process according to the invention was implemented with a vulcanized elastomer of natural rubber type. The particle size distribution was between 0.5 and 5 mm.

The process was implemented using a co-rotating twin-screw extruder with an L/D ratio of 68, which includes a receiving section with a length equal to 24 times the diameter of the extruder, including a grinding section with a length equal to 8 times the diameter of the extruder, a devulcanization section with a length equal to 8 times the diameter of the extruder and an outlet section with a length equal to 36 times the diameter of the extruder.

The rotation speed was 120 rom (rotations per minute).

The particles were introduced into the receiving section which was at a temperature of 140°C.

The particles were then ground within the grinding section at a temperature of 140°C which is located in the receiving section.

The particles were then subjected to shearing carried out in the devulcanization section at a temperature of 210°C.

The devulcanized material is then cooled and stabilized in the outlet section at a temperature of 80°C.

Devulcanization is confirmed by viscosity measurement

Mooney which indicates a value of 50 MU. The devulcanization rate indicates a value of 78% with a soluble fraction of 35%.

It is understood that the present invention is in no way limited to the embodiments described above and that many modifications may be made thereto without departing from the scope of the appended claims.

Claims (14)

1. A method for thermomechanically devulcanizing a vulcanized elastomer, comprising the following steps: - Providing a vulcanized elastomer in the form of particles having a predetermined size distribution, - Providing an extruder which comprises at least one rotatably mounted twin-screw, preferably co-rotatably mounted, which extends in at least 3 sections of said extruder, a receiving section located upstream, a devulcanization section and an outlet section located downstream, - Feeding said particles upstream of said extruder which is arranged to move said particles within it following a rotational movement of said at least one twin-screw, downstream thereof, towards said outlet section, - Optionally, grinding said particles in a grinding section to reduce the particle size, - Thermomechanical treatment of said particles in the devulcanization section to form a devulcanized material, - Feeding said devulcanized material to the outlet section to recover said ready-to-use devulcanized material, characterized in that said at least one twin-screw which extends into the devulcanization section is provided with at least one reverse-pitch screw element which is arranged to allow movement of the particles in the opposite direction, relative to the direction of movement of said particles fed upstream of said extruder, and a holding of the latter for a period of time sufficient to allow devulcanization and in that these particles fed in the opposite direction are thermomechanically treated after they have been in contact with said reverse-pitch screw element. 2. A method according to claim 1, wherein said particles are heated, preferably in the receiving or devulcanization section, the temperature being adjusted so as to reach a temperature sufficient to allow devulcanization. 3. A method according to claim 2, wherein said sufficient temperature applied at the level of the reverse pitch screw element is optionally the highest temperature applied relative to the temperatures prevailing in the other sections of said exiruder. 4. Method according to any one of the preceding claims, in which the devulcanized material is produced by means of the extruder at a flow rate of maximum 500 kg/h, preferably maximum 350 kg/h, more preferably maximum 300 kg/h, more preferably still maximum 250 kg/h, advantageously maximum 200 kg/h, more advantageously maximum 150 kg/h. 5. A method according to any preceding claim, wherein said at least one twin-screw located in the devulcanization section comprises at least 2 screw elements, a mixing screw element arranged to carry out the devulcanization followed by a reverse pitch screw element arranged to allow movement of the particles in the opposite direction for a sufficient period of time to carry out the devulcanization. 6. Method according to any one of the preceding claims, in which said at least one twin-screw of the extruder has a rotation speed, preferably under steady state, of between 50 and 600 rpm, preferably between 250 and 450 rpm, preferably between 300 and 400 rpm. 7. A method according to any preceding claim, wherein said particles move in the opposite direction by the effect of the reverse pitch screw element and are retained in the devulcanization section for a period of between 0.1 and 10 seconds, preferably between 1 and 6 seconds. 8. Method according to any one of the preceding claims, in which said particles have a residence time in the devulcanization section of between 0.1 and 4 seconds, advantageously corresponding to the duration of the devulcanization. 9. A method according to any preceding claim, wherein said devulcanization section corresponds to ONE module which has a length equal to 4 times the diameter of the extruder. 10. A method according to any preceding claim, wherein cooling of the devulcanized material is carried out in said outlet section, preferably to a temperature between 20 and 100°C. 11. A method according to any preceding claim, wherein the temperature applied within said devulcanization section is between 180 and 250°C. 12. Method according to any one of the preceding claims, in which said devulcanization section has a length of between 4 and 8 times the diameter of the extruder, preferably between 4 and 6, more preferably equal to 4. 13. Exiruder for thermomechanically devulcanizing a vulcanized elastomer, comprising at least one rotatably mounted twin-screw, preferably co-rotating, which extends in at least 3 sections, A reception section located upstream, a devulcanization section and an outlet section located downstream, said extruder being arranged to move the vulcanized elastomer in the form of particles within it following a rotational movement of said at least one twin-screw downstream thereof, in the direction of the outlet section, characterized in that said at least one twin-screw which extends into the devulcanization section is provided with at least one reverse-pitch screw element which is arranged to allow movement of the particles in the opposite direction, relative to the direction of movement of said particles brought upstream of said extruder, and a holding of the latter for a period of time sufficient to allow devulcanization and in that these particles brought in the opposite direction are thermomechanically treated after they have been in contact with said reverse-pitch screw element. 14. Exirudeuse according to claim 14, in which said at least one reverse-pitch screw element constitutes the last screw element of the devulcanization section which is preceded by a mixing screw element arranged to devulcanize the particles fed in the opposite direction and held by said at least one reverse-pitch screw element in order to be able to carry out the devulcanization.