FR3010084A1 - PROCESS FOR TREATING A SOLUTION OF PLASTIC MATERIAL IN A SOLVENT CONTAINING INSOLUBLE PARTICLES - Google Patents

Abstract

A process for treating a solution of plastic material in a solvent containing insoluble particles, said process comprising the following steps: - the particles are mechanically separated from the solution - their flow is caused through an enclosure provided with a lower orifice surrounded by a cap defining an internal volume separate from that of the chamber through which the particles also flow but leaving a free volume - it injects steam into the cap.

Description

The present invention relates to a process for the treatment of a plastic solution in a solvent containing insoluble particles.

Plastics are widely used in various forms, mainly in the solid state, for the manufacture of various items, flexible or rigid, such as for example tarpaulins, coated fabrics and other elements for the interior trim of vehicles , pipes, blisters (pharmaceutical packaging), window frames or electrical cables with polymeric insulation. However, it often happens that at a given moment of their existence, they are in solution in a solvent from which it is then necessary to extract them. Thus, we are confronted with polymer solutions at the end of certain polymerization processes (called "in solution"), during certain recycling processes, during the cleaning of certain object-making or paint-based installations. Thus, various methods of recycling plastics based on dissolution using organic solvents have been proposed. The patent application EP 945481 in the name of the applicant proposes for example a recycling process of an article based on at least one vinyl chloride polymer, according to which: (a) the article is shredded into fragments of an average dimension of 1 cm to 50 cm in case it exceeds these dimensions; (b) the dry article fragments are contacted with a solvent capable of dissolving the substantially anhydrous polymer, forming with water azeotrope (MEK preferably); (c) the precipitation of the polymer dissolved in the solvent is caused by the injection of water vapor into the solution thus obtained, which further causes the entrainment of the solvent-water azeotrope and thus leaves a mixture consisting essentially of water and solid particles of polymer; (d) the polymer particles are collected. Such a process generally also comprises at least one of the following steps: a: the fragments of articles are fed from a storage silo to a dissolver bl: the polymer solution is fed from the dissolver to a primary filter separating the insolubles from large size (typically reinforcements or accessories having at least a dimension> 150 μm) of the polymer solution b2: the insolubles are preferably treated to remove traces of polymer and residual solvent, which can be done by stripping at steam b3: the polymer solution is sent to a precipitator by prior passage through a centrifugal decanter to remove smaller insolubles c: the polymer particles from the precipitator are separated from the water and fed to a dryer to using a pump. Depending on the type of insoluble content in the article to be recycled, it may be advantageous to operate the steps b, bl, b2 and b3 in the same reactor, which is then a dissolver-filter. The application EP 2276801 in the name of the applicant describes a method using such an apparatus for recovering the fibers of an article to be recycled. This process consists of first cutting the article into fragments which are dissolved in a solvent; recovering the fibers of the solution; wash them with solvent; and lastly, to steam stripping them. Such steam stripping is relatively easy to achieve with insolubles in fiber form, but is significantly less with insolubles in the form of "shorter" and / or smaller particles. A problem that the Applicant has encountered in injecting the steam directly into these particles is the progressive clogging of the pipe for supplying the vapor by said particles.

Therefore, the present invention aims to provide a method for avoiding this disadvantage. To this end, the present invention relates to a process for a solution of plastic material in a solvent containing insoluble particles, comprising the following steps: - the particles are mechanically separated from the solution - their flow is caused through a chamber provided with a lower orifice surrounded by a cap defining an internal volume separated from that of the chamber through which the particles also flow - it injects steam into the cap.

The plastics material of the present invention may be of any kind. It may be an apolar polymer, such as a polymer of ethylene - (PE) or propylene (PP); styrene polymers such as PS (polystyrene) ABS (acrylonitrile-butadiene-styrene terpolymer). It may also be a polar polymer such as a polymer of vinyl chloride (PVC) or vinylidene chloride (PVDC), or a copolymer of ethylene and polyvinyl alcohol (EVOH). It can also be a mixture of such plastics of which at least one is in solution. Good results have been obtained with PVC. By PVC is meant any homo- or copolymer containing at least 50% by weight of vinyl chloride. Before being dissolved, the plastic material may be in any form. It may for example be waste polymerization, compounding or implementation, possibly in the liquid or pasty state, possibly even in solution in a solvent. It may also be solid articles (in the form of flexible or rigid pipes, containers, sheets for covering floors, tarpaulins, window frames, electrical cable insulation sleeves, etc.). ) comprising one or more usual additives such as, for example, plasticizers, stabilizers, antioxidants, flame retardants, pigments, fillers, etc., including reinforcing fibers. These fibers can be of any nature, natural or synthetic; it may be fiberglass, cellulose or plastic, such as polyester fibers and in particular, polyethylene terephthalate (PET) fibers. The insolubles contained in the solution (and generally present in the aforementioned articles) may be (fragments of) reinforcements (fibers, various fillers), "accessories" such as metal eyelets, labels, metal conductors, etc. ; plastic materials of another nature ... For example, waste electrical cables generally contain PVC and copper; roof membrane waste generally comprises PVC and PET fibers; Pharmaceutical blister waste generally comprises several different plastics (typically PVC and PE), which are not soluble in the same solvents; wallpaper waste often contains PVC and paper etc. by definition, these insolubles are present as solid particles in the solution. Note that there may be several types of insolubles as described above in the same solution. In a process where the choice of the solvent capable of dissolving the plastic is free (recycling process for example), it is preferably selected from liquids having a solubility parameter (a definition of which - 4 - and experimental values in "Properties of Polymers", DW Van Krevelen, 1990 Edition, pp.200-202, and in "Polymer Handbook", J. Brandrup and EH Irrunergut, Editors, Second Edition, pp.IV-337 to IV- 359) close to the solubility parameter of the plastic material to be dissolved and / or having strong interactions with it (hydrogen bonds for example). The term "neighbor" is generally equivalent to "not deviating more than 6 units". It is generally an organic solvent, preferably polar such as MEK (methyl ethyl ketone), which gives good results with many polymers and in particular with halogenated polymers such as PVC. It is understood that by solvent is meant both simple substances and mixtures of substances. In particular, in the case of a continuous and / or closed loop recycling process, the solvent may be a recycled liquid stream and may contain a certain amount of non-solvent. The non-solvent used in the process according to the invention generally has a solubility parameter different from that of the polymer to be recovered and does not have a strong interaction with it. The term "different" generally means that the difference between the solubility parameters of the non-solvent and the polymer exceeds 4 or even 6 units. A nonsolvent which is suitable (since it has a solubility parameter which is very different from that of most polymers and which is advantageous from an environmental point of view) is water, in particular when the polymer to be recovered is an ABS resin. a styrene polymer or PVC. Moreover, many plastic waste contains a significant amount of water which will therefore also be found in the environment and therefore, from this point of view, the choice of water as a non-solvent is also wise. According to the invention, the insolubles are mechanically separated from the plastic solution. It can be a filtration, a decantation, a centrifugation etc. The mechanical separation step can also take place by a mixed process, for example by filtration in a centrifugal decanter. By definition, it is an apparatus which combines the application of two different forces which depend both on the density of the bodies to be separated: the force of gravity and the centrifugal force. Such devices are in particular marketed by Alfa Laval, Pieralisi, Bord, Broadbent and Siebtechnik.

The process according to the invention can be carried out several times in series, on the mechanically separated solution of the particles in the preceding step, if necessary, and possibly varying the nature (the type) of the mechanical separation. Following the mechanical separation step according to the invention, there are two distinct products: the filtrate (or insoluble) on the one hand, and the purified solution on the other hand. This can advantageously also be treated to recover the plastic material. This recovery is advantageously by precipitation with a nonsolvent. In the case of the PVC / MEK couple mentioned above, the non-solvent is preferably water at least partly in the form of steam as described in the above-mentioned EP application, the contents of which for this purpose are incorporated by reference herein. request.

As for the filtrate (insoluble particles), it generally contains solution residues in an amount of the order of% by weight or even 10%%. According to the invention, it is subjected to a purification treatment in order to substantially remove these residues (for example to reach residual solvent contents of 50 to 100 ppm (parts per million by weight). The invention provides for the flow of particles through an enclosure provided with a lower orifice, which chamber may have any shape, cylindrical or funnel-shaped, and the particles out through a lower orifice, preferably located in the central portion of the bottom of the enclosure.This orifice is, in the case of a chamber in the form of a funnel, located at the end of a cylindrical portion extending a portion According to the invention, the lower orifice is surrounded by a cap defining an internal volume separated from that of the chamber, preferably the bottom of the chamber is in the form of a funnel and the cap surrounds preferably less partially the cylindrical part of this funnel. According to the invention, the particles also flow through the cap, preferably leaving a free volume (not traversed by the flow of the particles) for the expansion of the vapor. There is therefore preferably a free volume between the lower orifice of the enclosure and the lower wall of the cap. The lower part of the enclosure is thus somehow made of a double envelope. The cap (or outer shell) is preferably also provided with an orifice in its lower part (preferably also centrally located and substantially in the extension of the orifice of the enclosure), the flow rates of the particles both through the enclosure than through the cap being preferably optimized so as to maximize the efficiency of the stripping. For this, the steam is preferably introduced tangentially (ie tangentially to the flow of the particles) in order to aid the cleaning of the cap and to promote stripping.

Claims (10)

CLAIMS 1 - Process for the treatment of a solution of plastic material in a solvent containing insoluble particles, said process comprising the following steps: - the particles are mechanically separated from the solution - their flow is caused through an enclosure provided with a lower orifice surrounded by a cap defining an internal volume separated from that of the chamber through which the particles also flow - one injects steam into the cap. 2 - Process according to claim 1, wherein the plastic material is a polymer of vinyl chloride (PVC) and the solvent is MEK (methyl ethyl ketone). 3 - Process according to any one of the preceding claims, said process being performed several times in series, on the mechanically separated solution of the particles in the previous step, if necessary, and possibly varying the nature of the mechanical separation. 4 - Process according to any one of the preceding claims, wherein the bottom of the enclosure has the shape of a funnel comprising a conical portion and a cylindrical portion and wherein the cap preferably surrounds at least partially the cylindrical portion. 5 - Process according to any one of the preceding claims, wherein the cap is also provided with an orifice in its lower part. 6 - Process according to the preceding claim, wherein the orifice in the cap and that of the enclosure are located centrally and substantially in the extension of one another. 7 - Process according to any one of the preceding claims, wherein the mechanically separated solution of the particles is treated to recover the plastic material. 8 - Process according to the preceding claim, wherein the recovery of the plastic material is by precipitation using a non-solvent 9 - Process according to the preceding claim, wherein the non-solvent is water at least in part under aeia of vapor. 10 - Process according to any one of the preceding claims, wherein the steam is injected tangentially into the cap.