LU88522A1 - Treatment of PET waste and conversion into new prods. - by taking waste chippings and eliminating water microparticles and pre-crystallising in dry heated air flow, melting at optimal fluidisation temp. and degenerating - Google Patents

Abstract

Method of recycling objects composed of thermoplastic polymers, partic. PET, comprises several prepn. phases of the thermoplastic to transform it into a prod. based on chippings free of pollutant agents, elimination of any aq. microparticles and the exposure of the chippings to dehydration at a temp. of optimal fluidisation to form a homogeneous prod., deaeration of fluidised prod., extrusion after dehydrated and deaerated prod., and cooling at a predetermined temp. to obtain optimal crystallinity. Also claimed is a recycling installation of a thermal treatment stage and a thermoplastic polymer extruder with a screw profile designed to give deaeration in the melt.

Description

PROCESS AND PLANT FOR RECYCLING OBJECTS COMPOSED OF A THERMOPLASTIC POLYMER

The present invention relates to a method and an installation for the recycling of objects composed of a thermoplastic polymer.

It is known that the recycling of the material making up objects of any shape (for example bottles for containing and transporting liquids), produced with thermoplastic polymers, for example with a saturated polyester resin, which can be polyethylene terephthalate (PET), normally makes it possible to obtain a product composed of a plurality of chips of the recycled material, practically free of polluting elements, such as for example glues, cardboard and other foreign products originally found on the object whose material has just been recycled.

The chips thus obtained can be reused if they are added, in greater or lesser proportions, depending on the requirements, to a virgin product (for example PET) for the production of new objects.

The fact that said chips (recycled PET) cannot be used in a minimal part comes mainly from the fact that their chemical and physical characteristics are lower than those of the virgin product, thus not admitting their 100% reuse but only a partial reuse, guaranteeing all types of treatment for which the recycled material is primarily intended.

It is moreover easily understandable that the material composing the object using chips of recycled material and virgin material will always lend itself more difficultly to successive recycling.

In this situation, it is easy to understand that the use of a percentage of chips of recycled product (recycled PET) however leads on the one hand to a decrease in the chemical and physical properties of the material composing the new object compared to the properties of virgin material , as well as the corresponding possible drawbacks during treatment, without, on the other hand, allowing a significant reduction in the costs of production of the objects produced only partially with recycled material.

In this situation, the technical task to be fulfilled by the present invention consists in remedying the above technical drawbacks.

Within the framework of this technical task, an important objective of the present invention consists in providing a method and an installation for the recycling of objects composed of a thermoplastic polymer, in which the recycled thermoplastic polymer (for example PET) is reused almost completely for the production of new objects.

Another objective of the invention consists in carrying out a process and an installation for the recycling of objects composed of a thermoplastic polymer, making it possible to produce the same objects as those produced with a virgin non-recycled material.

An additional objective of the invention consists in carrying out a method and an installation for the recycling of objects composed of a thermoplastic polymer, making it possible to produce a product having chemical and physical characteristics really superior to those of the virgin product by the fact that 'It underwent, during the recycling process, a better crystallization, having resulted in an improvement of its processing capacities thanks to the improvement of the flexibility and the resistance of the material.

A final important objective of the invention consists in providing a process and an installation for recycling objects made of a thermoplastic polymer, having a high ecological value and allowing, in addition, a significant reduction in the costs of manufacturing recycled industrial products for consumption. current.

The technical task indicated and the specified objectives are essentially fulfilled by a process for the recycling of objects composed of a thermoplastic polymer comprising several stages of preparation of the thermoplastic polymer being recycled, to transform it into a compound basic product. of chips free of pollutants, characterized in that it comprises the elimination of said chips the aqueous microparticles which they contain, the exposure of said dehydrated chips to an optimal fluidization temperature Tf to form a homogeneous product, the deaeration of said fluidized product, the extrusion of said fluidized and deaerated product and its cooling after extrusion, to a predetermined temperature, to achieve optimal crystallization.

Said method can be carried out with an installation for recycling an object composed of a thermoplastic polymer, comprising at least one machine for performing a heat treatment and at least one machine for extruding the thermoplastic polymer, comprising an inlet orifice and an outlet orifice for said thermoplastic polymer, heating means for melting said thermoplastic polymer to a predetermined degree of fluidity, means for mixing and conveying said thermoplastic polymer from said inlet orifice to said orifice outlet, near which a die is arranged, and deaeration means of said polymer, arranged between said inlet orifice and said outlet orifice, characterized in that said mixing and conveying means are defined by a screw variable pitch extrusion, for the variation of the conveying speed and the pressure of said polymer the rmoplastic between said inlet orifice and said deaeration means and between said deaeration means and said outlet orifice.

Other characteristics and advantages of the invention will emerge / on the basis of the description of a preferred but not exclusive embodiment of a method and an installation for the recycling of objects composed of a thermoplastic polymer according to the invention, illustrated by way of indication and not limitation in the accompanying drawings, in which: FIG. 1 is a schematic view in side elevation of the machine for extruding the thermoplastic polymer according to the invention; and Figure 2 is a detailed view of the extrusion screw according to the invention.

The object composed of a thermoplastic polymer first undergoes a series of treatments to rid it of the polluting agents which it may contain, for example cardboard, glues and other similar agents, until obtaining 'A product composed of a thermoplastic polymer, for example a saturated polyester resin, more specifically polyethylene terephthalate or its derivatives (PET), in the form of chips and powder.

During a successive phase, the mechanical separation of the shavings from the powder takes place, by means of a sieving operation, so as to obtain a basic product composed entirely of shavings, for example PET.

During a successive phase, the chips are subjected to a dehydration treatment to remove from them any aqueous microparticles that they contain.

It has been found that during this dehydration phase, the temperature enabling the best results to be obtained is between -35 ° C and - 65 ° C.

The optimum temperature determined is preferably -50oC.

In the case where it is desired to save energy, without reaching the above temperature, it is possible to carry out a heat treatment beforehand of the chips, in order to eliminate to a large extent the amount of the aqueous microparticles they contain.

In this case, the preliminary heat treatment will be carried out at a temperature of between 35 and 70 ° C., preferably at a temperature of 55 ° C.

After removal of any polluting element from the chips and after their dehydration, they are exposed to an optimal fluidization temperature Tf to form a homogeneous product which will be deaerated during a successive phase, and, after having been fluidized and deaerated as indicated above, subjected to extrusion before being cooled, after extrusion, to a predetermined temperature in order to achieve optimal crystallization.

The crystallization temperature is for example between 5 and 20 "C, it is preferably of the order of 12eC.

During the fluidification, deaeration and extrusion phases, the homogeneous product is preferably subjected to a practically continuous mixing operation, in the presence of a predetermined temperature and pressure, as described in more detail below. .

It should also be noted that during this mixing operation, the homogeneous product must have a degree of fluidity which remains practically constant over time.

It should be noted in particular that during a first mixing phase, the homogeneous product, composed for example of PET, is subjected to a pressure PI and to a set theoretical temperature T1, the value PI being practically between 20 and 80 bars, and preferably being almost equal to 50 bars, the temperature T1 being between 265 and 285 ° C, preferably practically equal to 275eC.

During the second phase of mixing the homogeneous product, it is exposed to a pressure P2 of between 30 and 50 bars, preferably practically equal to 40 bars, and to an established temperature T2 of between 255 and 275 ° C, preferably practically equal to 265 ° C.

During a third mixing phase, the homogeneous product is exposed to a pressure P3 between 60 and 150 bars and to a temperature T3 between 260 and 280eC, preferably practically equal to 270 * 0.

The deaeration phase of the product is carried out in the presence of temperature T2 and pressure P2.

The extrusion phase of the fluidized and deaerated product is carried out on the other hand in the presence of a pressure P4 between 150 and 250 bars, on average equal to 200 bars, and at an established temperature T4 between 265 and 285 ° C, preferably practically equal to 275 ° C.

The conveying speed of the thermoplastic polymer, in particular PET, is also preferably lower when the product is transferred to the deaeration phase, while it increases after this last phase, when the product is transferred to the phase extrusion.

The example below is used to illustrate the invention by way of explanation but not limitation.

Example I

100 kg of chips mixed with powder are used, for example of the type PET 07333 from the company RETECH, P.O.B. 191 61 90 AD BEEK, The Netherlands, for example from containers of polyethylene terephthalate or its derivatives (PET).

The PET fragments are introduced for 5 minutes inside a mechanical type dust collector with an oscillating vacuum screen. The chips thus separated from the powder are then transported by conventional means to a dehumidification device for said chips for a time between 4 and 6 hours, at a temperature between 90 and 160 ° C.

The dehydrated chips are then introduced into a metering device, type DTM 200, produced by TECNOTRADING srl, of S. Maria du Sala (VE), in order to produce a quantity of chips of 1.670 grams (with reference to the 100 kg of the example) per minute in an extrusion machine, the extrusion screw of which rotates at a speed of 80 revolutions per minute.

The product then crosses a die, for example with 12 holes, before being immediately cooled by immersion in a fluid at a temperature of 12 ° C for about 4 seconds.

This achieves perfect and homogeneous crystallization of the product which will then be cut with a cutting machine, type T 150, produced by MECCANOPLASTICA di Mazza & C s.a.s. of Castiglione Olona (VA), for final storage.

Example II

100 kg of chips mixed with powder are used, for example of the type PET 07333 from the company RETECH, P.O.B. 191 61 90 AD BEEK, The Netherlands, for example from containers of polyethylene terephthalate or its derivatives (PET).

The PET fragments are introduced for 5 minutes inside a mechanical type dust collector with an oscillating vacuum screen. The shavings thus separated from the powder are preheated to about 350 ° C for about 4 seconds.

The preheated chips are then transported by traditional means to a dehumidification device for said chips, carried out for 30 minutes at a temperature between 90 and 160 ° C.

The dehydrated chips are then introduced into a metering device, type DTM 200, produced by TECNOTRADING srl di S. Maria di Sala (VE), with a view to producing a quantity of chips of 1.670 grams (with reference to the 100 kg of the example ) per minute in an extrusion machine, the extrusion screw of which rotates at a speed of 80 revolutions per minute.

The product then crosses a die, for example with 12 holes, before being immediately cooled by immersion in a fluid at a temperature of 12 ° C for approximately 4 seconds.

We thus achieve a perfect and homogeneous crystallization of the product which will then be cut with a cutting machine, type T 150, produced by MECCANOPLASTICA di Mazza & C. s.a.s. of Castiglione Olona (VA), for final storage.

/ t

The process described above is carried out with an installation for recycling an object composed of a thermoplastic polymer comprising at least one machine for performing a heat treatment and at least one machine for extruding the thermoplastic polymer.

The extrusion machine, generally designated by the reference number 1, has an inlet port 2 and an outlet port 3, near which is arranged a die 4 through which the thermoplastic polymer is passed.

The extrusion machine has in particular heating means 5 for melting the thermoplastic polymer to a predetermined degree of fluidity, means for mixing and conveying 6 the thermoplastic polymer from the inlet orifice to the orifice. outlet, and deaeration means 7 of the thermoplastic polymer, arranged between the inlet orifice and the outlet orifice.

The mixing and conveying means are preferably defined by an extrusion screw, designated by the reference number 8, designed so as to allow the variation of the conveying speed and of the pressure of the thermoplastic polymer between the inlet port and the deaeration means 7 and between the latter and the outlet port 3.

The extrusion screw actually has a first zone "A" comprising members for controlled supply of the thermoplastic polymer, generally indicated by the reference number 9, a second zone "B", comprising depositing members and first members for transporting the thermoplastic polymer, generally designated by the reference number 10, a third zone "C", comprising members for deaerating the thermoplastic polymer, generally designated by the reference 11 and a fourth zone "D", comprising second transport members 12 of the deaerated thermoplastic polymer towards the die 4.

The controlled feeding members are in particular defined by a channel 13 extending helically in the first zone "A" of the extrusion screw and communicating with the inlet orifice 2.

The depositing members include an arcuate wall 14 defining a pocket 25. arranged near the helical channel 13, in order to be able to take the thermoplastic polymer leaving it in a predetermined quantity and to transport it, via the first transport elements, to deaeration elements 11.

The transport members are in particular defined by a thread 15 defining a pitch of the screw equal to PI.

As is clear from FIG. 2, the channel of the cylinder (that is to say the channel determined by the distance of the diameter Dv of the extrusion screw and the diameter De of the cylinder 26 in which it moves ) also progressively decreases when approaching the deaeration devices.

The pressure to which the thermoplastic polymer is exposed thus increases from the inlet 2 until it reaches maximum levels near the deaeration devices 11.

The deaeration members include an annular projection 16, followed by an expansion chamber 17, in which an expansion of the thermoplastic polymer takes place, with the gases it contains escaping, the latter being expelled via a degassing device 18 to the outside of an extrusion machine during the transportation of the thermoplastic polymer.

The second transport members, comprising a thread 19 with a pitch P2 of the extrusion screw greater than the pitch PI described above, come into action from the expansion chamber 17.

The difference between the step PI and the step P2 thus determines a speed of transport of the thermoplastic polymer in front of the expansion chamber 17 lower than the speed of transport behind the expansion chamber 17.

Behind the expansion chamber 17, the depth of the cylinder channel also progressively decreases towards the die 4.

Maintaining a constant fluidity of the thermoplastic polymer inside the extrusion machine is achieved by means of the heating means establishing a different temperature between the first and the fourth zone of the extrusion screw. /

These heating means can be constituted by incandescent resistors or, according to the invention, by high frequency magnetic inductors, so as to allow considerable energy savings.

The invention thus meets the defined objectives and has many important advantages, as indicated above.

The invention thus conceived can undergo numerous modifications and variations, all included within the framework of the concept of the present invention.

All the elements can also be replaced by technically equivalent elements.

The materials used, the shapes and the dimensions can be of any type, adapted to the requirements.

Claims (21)

1. Process for the recycling of objects composed of a thermoplastic polymer, comprising several stages of preparation of the thermoplastic polymer being recycled, to transform it into a basic product composed of shavings free of pollutants, characterized in what it includes the elimination of said chips from the aqueous microparticles which they contain, the exposure of said dehydrated chips to an optimum fluidization temperature Tf to form a homogeneous product, the deaeration of said fluidized product, the extrusion of the said fluidized and deaerated product and its cooling after extrusion to a predetermined temperature to achieve optimal crystallization. 2. Method according to claim 1, characterized in that said phases of preparation of said thermoplastic polymer comprise at least one phase of mechanical separation of said chips from the powder produced during their production, by means of an operation of vacuum screening. 3. Method according to claims 1 and 2, characterized in that said removal of the aqueous microparticles for the dehydration of said chips is carried out by subjecting them to at least one heat treatment for cooling. 4. Method according to one or more of the preceding claims, characterized in that said cooling heat treatment is preceded by at least one prior heat treatment of said chips. 5. Method according to one or more of the preceding claims, characterized in that during said phases of fluidification, deaeration and extrusion, said homogeneous product is subjected to a practically continuous operation of mixing, in the presence of a predetermined temperature and pressure. 6. Method according to one or more of the preceding claims, characterized in that during said mixing operation, said homogeneous product has an almost constant degree of fluidity. 7. Method according to one or more of the preceding claims, characterized in that during a first mixing phase, said homogeneous product is exposed to a pressure PI and to a temperature T1, during a second phase of mixing at a pressure P2 and at a temperature T2, lower than said pressure PI and at said temperature T1, and during a third phase at a pressure P3 higher than P2 but lower than PI, and at a temperature T3 higher than temperatures T2 and Tl. 8. Method according to one or more of the preceding claims, characterized in that said deaeration phase of said product is carried out in the presence of a pressure and a temperature equal to P2 and T2. 9. Method according to one or more of the preceding claims, characterized in that said extrusion phase is carried out in the presence of a pressure P4 greater than PI, P2, P3 and at a temperature T4 greater than T1, T2 and T3 . 10. Method according to one or more of the preceding claims, characterized in that said thermoplastic polymer is a saturated polyester resin or more precisely a polyethylene terephthalate or one of the corresponding derivatives. / 11. Method according to one or more of the preceding claims, characterized in that the speed of delivery of said product to said deaeration phase is less than the speed of delivery to said extrusion phase. 12. Installation for recycling an object composed of a thermoplastic polymer, comprising at least one machine for performing the heat treatment and at least one machine for extruding the thermoplastic polymer, comprising an inlet port and an outlet port of said thermoplastic polymer, heating means for melting said thermoplastic polymer to a predetermined degree of fluidity, means for mixing and conveying said thermoplastic polymer from said inlet orifice to said outlet orifice, near which is arranged a die, and deaeration means of said polymer, arranged between said inlet orifice and said outlet orifice, characterized in that said mixing and conveying means are defined by a variable pitch extrusion screw , for the variation of the conveying speed and the pressure of said thermoplastic polymer between said inlet orifice e and said deaeration means and between said deaeration means and said outlet orifice. 13. Installation according to claim 12, characterized in that said extrusion screw has a first zone comprising members for controlled supply of the thermoplastic polymer and a second zone comprising depositing members and first members for transporting said thermoplastic polymer to a third zone, comprising members for deaerating said thermoplastic polymer, as well as a fourth zone comprising second members for transporting said deaerated thermoplastic polymer to said die. 14. Installation according to one or more of the preceding claims, characterized in that said controlled supply members are defined by a helical channel communicating with said inlet orifice. 15. Installation according to claim 13, characterized in that said deposition members comprise an arcuate wall arranged on said screw, from which extend said transport members. 16. Installation according to claim 13, characterized in that said transport members have a thread defining a pitch PI of said screw and a depth of the cylinder channel which gradually decreases with the approach of said deaeration members. 17. Installation according to claim 13, characterized in that said deaeration members comprise an annular projection followed by an expansion chamber of said thermoplastic polymer, comprising a degassing device for expelling the gases produced in said channel during the routing of said thermoplastic polymer. 18. Installation according to claim 13, characterized in that said second transport members comprise a thread defining a pitch P2 of said screw and a depth of the cylinder channel which gradually decreases with the approach of said die. 19. Installation according to claim 13, characterized in that the pitch PI of said screw determines a conveying speed of said thermoplastic polymer lower than the conveying speed determined by said pitch P2 of said screw. 20. Installation according to claim 13, characterized in that said heating means establish a different temperature between said first and fourth zones of said screw. 21. Installation according to one or more of the preceding claims, characterized in that said heating means are high frequency magnetic inductors.