EP4114633A1

EP4114633A1 - Process for separating polymer materials from an assembly of elements

Info

Publication number: EP4114633A1
Application number: EP21714930.1A
Authority: EP
Inventors: Jean-Luc Schnitzler; Jennifer RAVEREAU
Original assignee: Suez International SAS
Current assignee: Suez International SAS
Priority date: 2020-03-02
Filing date: 2021-03-02
Publication date: 2023-01-11
Also published as: FR3107658A1; WO2021176174A1; FR3107658B1

Abstract

A process for separating polymer materials, comprising the following steps: a) a support (18) at least partially coated with a thermoplastic polymer (20) is provided, said thermoplastic polymer having a given glass transition temperature Tg; b) the temperature of said thermoplastic polymer (20) is reduced to a temperature Tinf lower than said glass transition temperature Tg of said thermoplastic polymer; c) said thermoplastic polymer (20) is mechanically treated at said temperature Tinf in order to detach said thermoplastic polymer from said support; and d) said detached thermoplastic polymer (20) is recovered.

Description

DESCRIPTION

Title of the invention: Process for separating polymer materials from an assembly of elements

The present invention relates to a process for separating polymeric materials from elements of an assembly.

[0002] One field of application envisaged is in particular that of recycling liquid filtration modules. These each comprise a framework made of first polymeric materials and a filter membrane made of a second polymeric material having a porous structure.

[0003] The filtration of water makes use of techniques and materials enabling them to be implemented. These techniques essentially consist in filtering this water by means of a porous membrane, the pore size of which depends on the application and the treatment or performance objectives to be achieved. It is indeed different for water desalination, wastewater treatment or drinking water treatment. The size of the pores is, for example, of the order of 20 nm. These membranes thus allow the passage of water molecules and retain chemical or biological particles in suspension larger than the size of the pores, such as viruses and bacteria for example. These porous membranes can have various structures and morphologies. In general, a distinction is made between tubular membranes and flat membranes.

[0004] These membranes are generally made of a technical polymer material with high added value, for example poly (vinylidene fluoride) or PVDF. PVDF has the advantage of being resistant to a wide range of chemical compounds and this is one reason it is popular for use as a filter.

[0005] The membranes of tubular shape can in certain cases be coated with a support, for example braided PET threads. The water is thus filtered radially from the outside to the inside of the membrane, then it flows longitudinally along the support wires.

These tubular membranes associated with the other frame elements, thus constitute filtration modules allowing in particular, the realization of a stage of clarification, or even disinfection, on water treatment installations and processes.

When these filtration modules cease to be effective, in particular because of the irreversible clogging, or the degradation of the polymers which constitute them, they are interchanged, and the modules at the end of their life or at the end of their life are then, either buried or incinerated, which, in the case of fluorinated polymers such as PVDF, releases hydrofluoric acid which should be neutralized.

Thus, on the one hand, more or less dangerous compounds are disseminated in nature, and on the other hand, we deprive ourselves of polymer materials with relatively high added value, especially in the case of Poly (vinylidene fluoride) , the costs of which are relatively high.

[0009] A problem which then arises and which the present invention aims to solve is to provide an inexpensive and efficient process which makes it possible to recover the polymer materials with high added value from assembled elements.

In order to solve this problem, there is proposed a process for separating polymeric materials, comprising the following steps: a) providing a support coated at least partially with a thermoplastic polymer, said thermoplastic polymer having a temperature of glass transition T _g given; b) the temperature of said thermoplastic polymer is lowered to a temperature T _inf lower than said glass transition temperature T _{g of} said thermoplastic polymer; c) said thermoplastic polymer is mechanically treated at said temperature Ti _nt to detach said thermoplastic polymer from said support; and, d) recovering said detached thermoplastic polymer.

Thus, a characteristic of the invention lies in taking into account the glass transition temperature T _g of the polymer material, in order to bring the temperature of the polymer material to a temperature below this before subjecting it to mechanical processing. In this way, the polymer becomes more brittle and it can then more easily break into pieces when subjected to the mechanical treatment. For example, in the case of a membrane comprising a braided support, in particular made of PET, coated at least partially with polymer material, said polymer material can be easily detached from the support and recovered by means of the process according to the invention, as is done. will explain below. "Thermoplastic polymers" are well known to those skilled in the art. In the present invention, fluorinated polymers such as PVDF or PTFE are more particularly envisaged, but also polyethersulfone (PES) or polypropylene (PP).

In the present invention, the "support" is generally itself a polymer material.

For the purposes of the present invention, a "mechanical treatment" means an interaction by contact with the polymer in order to be able to separate it from its support. According to a particularly advantageous embodiment of the invention, in step b), said temperature Ti _nt is less than 240 K. In this way, the temperature of the thermoplastic polymer is for example lowered to 230 K .

According to a first variant embodiment, in step b), said support coated with said thermoplastic polymer is immersed in liquid nitrogen. Thus, the boiling point of nitrogen in the liquid state being 77.36 K, when the thermoplastic polymer is immersed therein, its temperature drops suddenly below its glass transition temperature. It will in fact be observed that very few polymers, and in particular those used in filtration membranes, have a glass transition temperature of less than 150 K. Therefore, the polymer quickly becomes brittle, and without waiting for it to reach the temperature of the liquid nitrogen, it can undergo a mechanical treatment after immersion in order to be able to be detached from its support. Advantageously, the temperature T _inf is between 240 K and 100 K, preferably between 220 K and 195 K.

[0017] Also, the immersion time must make it possible to rapidly lower the temperature of the polymer directly exposed to liquid nitrogen, without however lowering the temperature of the support material too much if the latter is a polymer material, at the risk that he himself becomes more fragile. It will be observed that thermoplastic polymers do not all exhibit the same behavior when their temperature is lower than that of their glass transition and that some are more resistant to it than others. In addition to their nature, polymers exhibit behaviors which also vary depending on the additives they contain and their method of use.

On the other hand, liquid nitrogen is available very inexpensively, and therefore, the cooling step is inexpensive. Advantageously, in step c), said support coated with said thermoplastic polymer is crushed to detach said thermoplastic polymer from said support. Thus, by crushing the assembly, polymer and support, the detachment of the polymer from its support is caused. We then place ourselves in the aforementioned situation, where the material of the support, when it is a polymer, does not behave in the same way as the thermoplastic polymer in order to be able to detach the first from the second and easily separate the two materials. It will also be observed that when the support is made of braided threads, its morphology is different from the porous layer of PVDF which covers it.

[0020] Indeed, during crushing, the only thermoplastic polymer breaks at the level of the bond with the support and comes off easily.

Preferably, in step c), said support coated with said thermoplastic polymer is crushed between two rollers. The two rollers bear tangentially along a common generatrix, and the coated support is engaged between the two rotating rollers. Such an embodiment is preferred when the coated supports extend longitudinally, for example, when they are threads coated with the thermoplastic polymer to be recovered. As will be explained in more detail in the remainder of the description, a plurality of pairs of successive rollers can be used to detach the polymer material from the support.

According to a second variant embodiment, dry ice is projected against said thermoplastic polymer to simultaneously lower the temperature and mechanically treat said thermoplastic polymer according to steps b) and c). Thus, according to this second variant, dry ice is used, that is to say C0 ₂ in solid form, typically in the form of granules or sticks, the sublimation temperature of which is 195, 6 K. The dry ice, in the form of granules or sticks, is then projected at high speed against the coated support, which provides the double advantage of cooling the thermoplastic polymer covering the support, and moreover of striking the polymer then cooled with high kinetic energy, to detach it from its support. In many examples, dry ice makes it possible to lower the temperature of the thermoplastic polymer undergoing the impact, below its glass transition temperature, and hence the impacts of the dry ice themselves cause the detachment and separation of the material. polymer of its support. Thus, according to this embodiment, steps b) and c) are simultaneous. Another advantage of dry ice is that it leaves no residue in the thermoplastic polymer, since it turns into gaseous carbon dioxide and escapes into the atmosphere when the materials return to room temperature. For example, dry ice is projected against said thermoplastic polymer at a speed greater than 200 ms ¹ . Advantageously, the speed of the granules or rods is close to 300 ms ¹ , which produces a high kinetic energy of impact. Typically, the speed of the projected dry ice is less than 340 ms ¹ , preferably less than 320 ms ¹ .

According to one embodiment of the method according to the invention, in step a), a support is provided comprising a plurality of wire braids respectively coated with said thermoplastic polymer. Braided supports, for example made of PET, are covered with a porous tubular filter layer constituting the membrane. These coated supports thus constitute the hollow fibers. When the temperature of the thermoplastic polymer is lowered below its glass transition temperature, it then easily fragments when it is mechanically deformed, regardless of the mode.

[0026] Also, according to an alternative embodiment, the support comprises a plurality of films or multilayer plates.

According to a preferred embodiment, in step a), a support is provided comprising a plurality of braids of poly (ethylene terephthalate) yarns. And, advantageously, said thermoplastic polymer which covers it is poly (vinylidene fluoride). It will be observed that this thermoplastic polymer can cover other wire supports to form filtration membranes.

In addition, the thermoplastic polymer material can also be used on flat supports to form filtration membranes.

[0029] Also, according to yet another variant embodiment, the method according to the invention is implemented to collect the PVDF from the “backsheets” of photovoltaic panels. A layer of PVDF then covers a flat support, typically of PET. By lowering the temperature of the PVDF to a temperature below its glass transition temperature, it causes cracking and detachment from the PET support. Furthermore, and according to another embodiment, in step a), said thermoplastic polymer is poly (difluoromethylene). In other words, the thermoplastic polymer is PTFE.

[0031] Other features and advantages of the invention will become apparent on reading the description given below of particular embodiments of the invention, given as an indication but not limited to, with reference to the accompanying drawings in which:

[Fig. 1] is a schematic front view of an organ capable of being treated according to a method according to the invention;

[Fig. 2] is a detailed schematic view of the member illustrated in the figure [Fig. 1];

[Fig. 3] is a schematic view of a device for implementing the method according to the invention in accordance with a first variant embodiment;

[Fig. 4] is a detailed schematic view of the device illustrated in FIG. [FIG. 3] in operation;

[Fig. 5] is a flowchart illustrating the steps for implementing the method according to the invention in accordance with the first variant embodiment; and,

[Fig. 6] is a flowchart illustrating the steps for implementing the method according to the invention in accordance with a second variant embodiment. The process for separating polymeric materials according to the invention applied to the recycling of filtration modules will be described in detail. In particular, these are end-of-life water filtration modules, or defective filtration modules intended for disposal.

The modules here taken as an example, an example 10 of which is shown in the figure [Fig. 1], each comprise bundles 12 of hollow fibers 15 which will be described in detail below. The beams 12 extend longitudinally in parallel between two heads, one upper 14, the other lower 16, over a length of between 1.50 m and 3 m, for example 2 m.

[0034] Figure [Fig. 2] shows in a straight section one of the hollow fibers 15. It comprises a braid 18 of son of poly (ethylene terephthalate), commonly referred to as PET according to its ISO code. The wire braid 18 is covered with a tubular layer 20 of Poly (vinylidene fluoride) or PVDF, which tubular layer 20 forms a porous and filtering membrane. It will be observed that the tubular layer 20 and the braid of threads 18 are more or less interpenetrated into one another.

The diameter d of the wire braid 18 is of the order of 2 mm while the thickness § of the tubular layer 20 is of the order of ten micrometers. The ends of the hollow fibers 15 including the support 18 and the tubular layer 20 forming a membrane, are respectively engaged in the upper 14 and lower 16 heads, and are connected in a sealed manner to collectors not shown.

Also, the heads 14, 16 include different polymer materials, and in particular acrylonitrile butadiene styrene, or ABS, polyurethane or ethylene-vinyl acetate, or EVA, or even PVC or l epoxy.

Among all the aforementioned polymers, there is one, PVDF, which is of very particular interest, even if it represents only a small percentage of the total mass of the module, for example between 5% and 15 %, and that it should be possible to separate it from other polymer materials in order to recover it. The fibers represent for example between 40% and 50% of the weight of the module and the remainder to 100% corresponds to the materials of the two heads.

It will be observed that PVDF is a semi-crystalline thermoplastic polymer whose glass transition temperature T _g is 233 K. And one of the merits of the invention is to have imagined lowering the temperature of the PVDF of the modules filtration to better detach it and thus recover it. This is because, in fact, when a thermoplastic polymer is brought to a temperature below that of its glass transition, it is generally made more fragile and brittle so that it breaks easily. And in this case, this is indeed the case with PVDF as will be illustrated in the examples below.

According to a first embodiment of the method according to the invention, dry ice is projected against the bundles 12 of hollow fibers 15 and therefore directly against the tubular layer 20 of PVDF. Dry ice indeed has a sublimation temperature of 195.6 K.

To do this, use is made of a suitable projection device as shown in the figure [Fig. 3]. It comprises a dry ice reservoir 22 inside which the dry ice is stored in the form of sticks with a diameter of 3 mm for example. The tank ends with a conical bottom, and a The metering mechanism delivers the ice cream sticks into a flow of compressed air supplied by a compressor 24. The flow of compressed air thus loaded with dry ice is guided through a projection duct 26 terminated by a projection nozzle 28.

Thus, for example, under an air pressure in the nozzle of 5 bar, and a flow rate close to 3 m ³ / h, the dry ice sticks reach at the outlet of nozzle 28 a speed of 300 m / s.

Reference will also be made to the flowchart of the figure [Fig. 5] to describe the different steps of said first mode of implementation.

Thus, according to a first preparation step 30 of the module as shown in the figure [Fig. 1], the two heads are kept parallel to each other in the same substantially horizontal plane so as to extend the bundles 12 of hollow fibers 15 in a chain above a recovery tank.

Then, in a double cooling and treatment step 32, the projection nozzle 28 is applied and maintained from above towards the bundles of hollow fibers and it is maintained substantially perpendicular to the bundle at a distance of between 20 cm and 50 cm for example. One then proceeds by successive scans from one head 14 to the other 16 so as to cover the entire surface defined by the chain beams.

According to another procedure, the bundles of hollow fibers are extended in a vertical direction. And in the same way, the projection nozzle 28 is applied and maintained perpendicular to the beams.

In this way, in a first phase the dry ice projected against the hollow fibers 15 contributes to lowering the temperature of the polymer material of the membrane. It is considered that after a few seconds of impact, the polymer material reaches a temperature Ti _nt located below its glass transition temperature, for example 220 K. As a result, it becomes fragile and brittle. Then, after these few seconds, the dry ice in the form of sticks projected at 300 m / s against the polymer material of the membranes plays a mechanical role and thus causes the bursting of the tubular layer of PVDF 20 of the membrane, as illustrated on the figure [Fig. 4] and, in addition, detach it from the wire braids 18. Figure [Fig. 4] partially shows the nozzle 28 from which escapes sticks 34 of dry ice which strike the polymer material of the membrane 36 covering a braid of threads 38. The polymer material of the tubular PVDF layer of the membrane 36 breaks and detaches into chips 40. In this way, the polymer material of the membranes, in the form of chips 40, is conveyed through the bundles of hollow fibers 15 into the drip tray below.

It will be observed that the flow of dry ice sticks 34 is sufficiently powerful to reach all the hollow fibers 15 in the thickness of the bundles. In addition, after having swept the entire surface of the bundles of hollow fibers 15 of the module 10, the latter is turned over so as to be able to sweep the opposite surface in the same way.

According to another variant embodiment, the projection nozzles are used simultaneously against the two opposite surfaces of said module 10. Also, such a variant embodiment is easily implemented when the bundle of hollow fibers is extended. in a vertical direction.

In this way, all the wire braids 18 of the bundles 12 of hollow fibers 15 of the module are freed of their tubular layer of PVDF 20 which is found in chips in the recovery tank.

In a final step 42, the chips of the polymer material are recovered in the recovery tank in order to be able to repackage it into usable polymer. It will be observed that the recovery tank also contains organic and inorganic impurities, in particular earth and sand, which inevitably adhered to the tubular membranes. However, they easily detach from the membranes upon impact of dry ice. And in addition, these impurities and these polymer material chips can then be easily separated. Furthermore, such a separation process can easily be automated, either by means of a robot equipped with a movable arm supporting the nozzle, or by means of movable tables and nozzles maintained substantially perpendicular to said movable tables, in fixed position.

According to a second embodiment of the method according to the invention, the temperature of the PVDF of the tubular layer forming a membrane is lowered and its mechanical treatment is carried out in two successive steps. Thus, according to an initial preparation step 44, referenced in the flowchart of FIG. [FIG. 6], the module 10 is dismembered as shown in the figure [Fig. 1] so as to detach the bundles 12 of hollow fibers 15 from the two heads 14, 16. In other words, the hollow fibers 15 are separated from the rest of the module 10.

Then, in an immersion step 46, the bundles of coated fiber son are immersed in liquid nitrogen. The boiling point of liquid nitrogen is 77.36 K. Consequently, the PVDF quickly reaches, after a few seconds of immersion, a temperature below that of its glass transition, for example 210 K. And hence , it becomes brittle and crumbly.

According to a mechanical processing step 48, the bundles of coated son are then driven, in the longitudinal direction of the son, through a pair of rollers. A drip tray is installed under the pair of rollers. The pair of rollers comprises two rollers bearing tangentially against one another along a common generatrix. The rollers are initially in contact with one another and they move away substantially from one another as the hollow fibers of the bundles pass, while maintaining a bearing pressure on these fibers. The rollers are rotated in opposite directions to each other so as to drive the hollow fibers of the bundles in translation as they crush them. Thanks to the pair of rollers through which the wires of the bundles pass, the tubular membrane of the support wire braids bursts and is detached from the braids. The fragments of the polymer material then travel by gravity into the recovery tank. In a final step 50, the fragments of the polymer are thus recovered, just as in the first embodiment, in order to be able to recondition it.

According to another variant embodiment, is installed downstream of the pair of rollers, scraping or scraping members, making it possible to better separate the tubular membrane fragments from the wire braids.

Claims

CLAIM

[Claim 1] i A process for separating polymer materials, characterized in that it comprises the following steps:

- a) providing a support (18) coated at least partially with a thermoplastic polymer (20), said thermoplastic polymer having a given _{glass transition temperature T g;}

- B) the temperature of said thermoplastic polymer (20) is lowered to a temperature Ti _nt lower than said glass transition temperature T _{g of} said thermoplastic polymer;

- C) said thermoplastic polymer is mechanically treated at said temperature T _inf to detach said thermoplastic polymer from said support; and,

- D) said detached thermoplastic polymer (20) is recovered.

[Claim 2] A separation process according to claim 1, characterized in that in step b), said temperature T _inf is less than 240 K.

[Claim 3] A separation process according to claim 1 or 2, characterized in that in step b), said support (18) coated with said thermoplastic polymer (20) is immersed in liquid nitrogen.

[Claim 4] A separation process according to any one of claims 1 to 3, characterized in that in step c), said support (18) coated with said thermoplastic polymer (20) is crushed to detach said thermoplastic polymer ( 20) of said support (18).

[Claim 5] A separation process according to claim 4, characterized in that in step c), said support (18) coated with said thermoplastic polymer (20) is crushed between two rollers.

[Claim 6] A separation process according to claim 1 or 2, characterized in that dry ice is sprayed against said thermoplastic polymer (20) to simultaneously lower the temperature and mechanically treat said thermoplastic polymer (20) according to the steps b) and c).

[Claim 7] A separation process according to claim 6, characterized in that said dry ice is projected against said thermoplastic polymer (20) at a speed greater than 200 ms ¹ .

[Claim 8] A method of separation according to any one of claims 1 to 7, characterized in that in step a), a support (18) is provided comprising a plurality of wire braids respectively coated with said thermoplastic polymer ( 20).

[Claim 9] A separation process according to claim 7, characterized in that in step a), a support (18) is provided comprising a plurality of braids of poly (ethylene terephthalate) yarns.

[Claim 10] A separation process according to any one of claims 1 to 8, characterized in that in step a), said thermoplastic polymer (20) is Poly (vinylidene fluoride).

[Claim 11] A separation process according to any one of claims 1 to 8, characterized in that in step a), said thermoplastic polymer (20) is Poly (difluoromethylene).