Method for treating used plastic parts to recover their constituents

Abstract

To apply the invention to treat a part made of used plastic comprising an organic filler and an inorganic filler, (A) pieces of the part to be treated are admixed with at least one water-immiscible organic solvent (S1), which is a good solvent for the plastic and is capable of solvating the organic filler and the plastic and of releasing the inorganic filler; (B) an aqueous solution of an agent for extracting the inorganic filler is added to the mixture obtained, the aqueous solution being capable of transferring the inorganic filler by liquid-liquid extraction from the mixture to the aqueous solution, the inorganic filler then being in the dissolved state in the aqueous solution; (C) the two immiscible phases obtained are collectively admixed with a water-immiscible solvent (S2) which is miscible with the solvent (S1) and is a poor solvent for the plastic and a good solvent for the organic filler, in order to precipitate, in at least one solid phase, the plastic in dispersed form, while leaving the organic filler in the mixture of solvents (S1) and (S2), constituting an organic liquid phase, and the inorganic filler remaining dissolved in the aqueous solution, constituting an aqueous phase; the solid plastic phase is recovered by solid-liquid separation; separated by their density difference, the organic filler and the inorganic filler respectively are isolated from each of the organic and aqueous phases obtained.

Description

METHOD FOR PROCESSING USED PLASTIC PARTS TO RECOVER THEIR CONSTITUENTS

[0001] The present invention relates to a process for treating used plastic parts to separate the organic and inorganic components present therein and to recover a regenerated plastic material, which can be used again.

[0002] Plastic parts consist not only of the plastic material itself, but also of both mineral and organic fillers (additives), which can constitute up to 65% of the total weight of the plastic material.

[0003] Examples include parts made of ABS (Acrylonitrile Butadiene Styrene) thermoplastic that contain fillers used, for instance, for their flame-retardant properties (Sb2O3, tetrabromobisphenol-A, etc.) or to modify the color or intrinsic properties of the thermoplastic (talc, CaCO3, silica, silicates, etc.). A wide range of fillers is permitted, with over 400 types identified by the ECHA (European Chemicals Agency). While many of these fillers do not pose a problem, the ultimate goal of plastic recycling is to remove them to erase all traces of the plastic's previous uses during the recycling process. This would allow the strictest quality criteria and standards to be met for applications using recycled plastics.

[0004] To separate plastics, such as thermoplastics, from their components, current methods generally aim to remove at least some of the fractions to facilitate the processing of the remaining material. It is important to note that the objective of this invention is not to destroy these components, but rather to fully recover the fillers, whether they be plastic material, inorganic fillers, or organic fillers.

[0005] The main techniques, noted below (1) to (7), which allow this, without altering or by partially altering the fractions, are summarized in Table 1 below: Leaching applies the principles of extractive hydrometallurgy to thermoplastic particles instead of ores. It involves dissolving the fillers present in the plastic, for example, with an acid in aqueous solution. However, this operation is hampered by the fact that the plastic contains and isolates the fillers from the acid intended to dissolve them. Depending on the leaching conditions, the plastic may therefore remain intact or be slightly altered. Solvation uses a solvent to induce the mobility of polymer chains without liquefying the plastic, allowing the extraction of fillers from the polymer matrix via solid-liquid separation, with the plastic remaining undamaged.Dissolution / precipitation is widely described in the literature and allows, through dissolution, the liquefaction of one or more thermoplastic materials with a specific solvent, followed by the precipitation of one or more polymers from the same family with a suitable non-solvent. This method is often used to separate mixtures of thermoplastic materials.

[0006] (4) and (5) For additives which interfere with pyrolysis or combustion, due to legal standards or risks of equipment degradation, depollution methods are required before chemical or thermal recovery (technique 4), such as monomer distillation or chemical treatment with acidic or basic reagents (technique 5).

[0007] (6) After dissolution, the use of a poor solvent is proposed to precipitate the plastic material and simultaneously extract an inorganic or organic filler with it.

[0008] (7) This technique, a variant of technique 3, involves solid-liquid separation processes on the dissolved plastic material (similarly to technique 2) to extract a mineral filler, followed by selective precipitation of the plastic material, leaving one or more problematic additives in solution.

[0009] Technique: Opening of the plastic material; Extraction of fillers; Fate of the plastic material; Objective 1: Leaching; Recovery of an inorganic filler and the plastic material; 2: Solvation; Solid-liquid separation; Recovery of an organic filler and the plastic material; 3: Dissolution; Precipitation; Separation of plastic materials; 4: Depolymerization; Distillation; Recovery of the monomer in an organic filler; 5: Dissolution; Dehalogenation; Precipitation; Recovery of the plastic material and organic fillers; 6: Dissolution; Precipitation of inorganic fillers by a suitable solvent; Separation of the plastic material and organic fillers; 7: Dissolution; Solid-liquid separation of inorganics; Selective precipitation of the plastic material; Separation of the plastic material and inorganic and organic fillers

[0010] To achieve the aforementioned objective of recycling used plastics, enabling the recovery of reusable plastics for industrial use as raw materials, and the precise extraction of both organic and inorganic fillers for disposal or reuse, the approach proposed according to the present invention offers an alternative to technique 7 described above. It suggests that instead of using solid-liquid separation to isolate inorganic fillers (i.e., suspended solid particles), a specific aqueous complexing and extracting solution is added to target a specific inorganic filler suspended in the solvent containing the thermoplastic material and the dissolved organic fillers. This operation can be defined as selective interfacial leaching to dissolve only one type of suspended solid in the phase containing the plastic material.This leaching process is combined with a liquid-liquid extraction that transfers the targeted, dissolved inorganic filler from the liquid phase containing the plastic and organic fillers. The subsequent step, involving selective precipitation of the plastic depleted of this inorganic filler, aims for the targeted recovery of organic fillers, which then remain in the solvent.

[0011] This thermoplastic recycling technique achieves its objective while offering the added advantages of being carried out under ambient temperature and pressure conditions, using solvents and reagents with a low environmental impact, that are economical and low in concentration. Furthermore, the process is designed to minimize capital and energy requirements, and also to reuse solvents and aqueous solutions in closed-loop recycling systems, thus making resource use more efficient.

[0012] The present invention therefore relates to a process for treating a used plastic part comprising at least one organic filler and at least one inorganic filler in order to recover separately: the regenerated plastic material, depleted in said organic filler(s) and in said inorganic filler(s); the organic filler(s); and the inorganic filler(s).

[0013] characterized by the fact that it comprises the following successive steps consisting of: adding to the part to be treated or to pieces thereof at least one organic solvent (S1), immiscible with water, a good solvent of said plastic material and being capable of solvating said or said organic fillers and said plastic material and of releasing said or said inorganic fillers, to obtain a mixture containing: in dissolved form, said plastic material and said or said organic fillers; and in solid suspended form, said or said inorganic fillers; adding to the mixture obtained in step (A) an aqueous solution of at least one extraction agent of said or said inorganic fillers, said aqueous solution being capable of transferring by liquid-liquid extraction said or said inorganic fillers from said mixture to said aqueous solution, said or said inorganic fillers then being in dissolved form in said aqueous solution;add to the set of the two immiscible phases thus obtained in step (B) at least one solvent (S2) immiscible with water, miscible with said at least one solvent (S1), poor solvent of said plastic material and good solvent of said or said organic fillers to precipitate, following at least one solid phase, said plastic material in dispersed form while leaving said or said organic fillers in the mixture of said at least one solvent (S1) with said at least one solvent (S2), composing an organic liquid phase, said or said inorganic fillers remaining dissolved in the aqueous solution, composing an aqueous phase;

[0014] recover said solid phase(s) of plastic material by solid-liquid separation; and

[0015] isolate from each of the said organic and aqueous phases obtained, separated by their difference in density, respectively said organic charge(s) and said inorganic charge(s).

[0016] Advantageously, the piece to be processed is reduced to pieces, in particular to a dimension in its narrowest section less than 1 cm, for example from 50 mm to 0.5 mm, before engaging it in step (A).

[0017] At step (A), the solvent or each solvent (S1) advantageously has a RED value of less than 1, preferably less than or equal to 0.25, relative to the Hansen sphere of the plastic material.

[0018] For this calculation of the RED value for the solvent(s) (S1) – and also for the solvent(s) (S2) as will be discussed below – refer to Hansen, CMHansen Solubility Parameters: A User's Handbook, 2nd ed.; CRC Press: Boca Raton, 2007. Pages 4 to 8, the dataset is available on HSPiP Datasets, Hansen Solubility parameters https: / / www.hansen-solubility.com / HSPiP / datasets.php.

[0019] At step (A), the mass proportion of solvent (S1): plastic material can be from 5:1 to 2:1.

[0020] Step (A) can be carried out at a temperature of 15 to 100°C or at the reflux temperature of the organic solvent (S1), in particular at a temperature of 15 to 40°C.

[0021] Step (A) can be conducted at an absolute pressure of at least 10 5 Pa (1 bar).

[0022] In accordance with particular embodiments of the process according to the present invention, in step (B), in the case of several inorganic feeds, an aqueous solution containing different extraction agents is used, at a ratio of one extraction agent for one inorganic feed considered in order to simultaneously dissolve said feeds, or several aqueous solutions containing each one extraction agent for one organic feed considered are used successively, said step (B) being able to be carried out at a temperature of 15 to 90°C.

[0023] In step (B), an aqueous solution containing at least one additive selected from surfactants, such as the nonionic polyoxyethylene surfactant marketed under the trade name Triton® X-100, and phosphatidylinoline, and phase-transfer catalysts, such as the quaternary ammonium salt marketed under the trade name Aliquat® 336 and tetrabutylammonium chloride, may be used, in concentrations, for example, of 10 -2 at 10 -4 mol.L -1 .

[0024] At step (C), the solvent or each solvent (S2) may have a RED value greater than 1, preferably greater than or equal to 1.25, relative to the Hansen sphere of the plastic material, and a RED value less than 1, preferably less than or equal to 0.75, relative to the Hansen sphere of the organic filler.

[0025] Step (B) can be followed by a separation step by filtration of insoluble materials.

[0026] One can mention in particular the process as defined above in which: the plastic material is a thermoplastic material, such as acrylonitrile-butadiene-styrene, polypropylene, polyvinyl chloride or high impact polystyrene; the organic filler(s) is or are selected from brominated flame retardants, such as tetrabromobisphenol-A; the inorganic filler(s) is or are selected from synergists of brominated flame retardants, such as antimony trioxide; the solvent(s) (S1) is or are selected from nitrobenzene, aniline, isoamyl acetate, n-butyl acetate, chloroform, dichloromethane, 2-phenoxyethanol, ethylbenzene, methyl isobutyl ketone and cyclohexanone; the solvent (S2) is diethyl ether; and the extraction agent is tartaric acid, citric acid or hydrochloric acid.

[0027] The process according to the present invention can be carried out in batches, semi-continuously or continuously.

[0028] The following example illustrates the present invention without, however, limiting its scope. It relates to the separation of the brominated flame retardant tetrabromobisphenol-A and the synergist of this retardant, which is antimony oxide Sb2O3, from ABS plastic material from waste electrical and electronic equipment, to recover: a fraction containing antimony; a fraction recovering the brominated molecules; and a fraction of ABS plastic material, here in the form of fibers, depleted of its original fillers. Preparatory stage

[0029] Under ambient conditions, ABS plastic sheets from electronic waste consisting of used computer screens were cleaned with MilliQ water and soap. Using wire cutters, the cleaned sheets were cut into 10 mm x 10 mm pieces, each weighing approximately 0.3 g.

[0030] Chemical analyses by X-ray fluorescence demonstrated the presence of 30,500 ppm of Sb2O3 and 90,500 ppm of tetrabromobisphenol-A.

[0031] Step A: Solubilization of ABS plastic

[0032] At 25°C and 0.1 MPa absolute (1 bar absolute), approximately 1 g of ABS pieces (three pieces of 0.3 g each on average) were placed in a 20 mL glass tube, which could be sealed with a hermetically sealed polypropylene stopper. 10 mL of dichloromethane was then added to the tube, which was then sealed and shaken on a reciprocating shaker at 200 movements per minute for 3 hours.

[0033] The solvent dissolved the ABS and tetrabromophenol-A, while the solid Sb2O3 was released from the plastic material and suspended in the liquid.

[0034] Step B: Liquid-liquid extraction of the inorganic feedstock Sb2O3

[0035] At room temperature and ambient pressure, 10 mL of an aqueous solution of 0.1M tartaric acid was added to the tube as an extraction agent, to leach the solid antimony oxide Sb2O3 and perform a liquid-liquid extraction from the dichloromethane solvent to the aqueous solution.

[0036] For this purpose, the tube was hermetically sealed and placed on the shaker at the same frequency for 96 hours.

[0037] During this process, Sb2O3 is transferred into the aqueous phase, forming a complex through the following reaction:

[0038] Sb2O3(s) + 2C4H6O6(aq) -> Sb2(C4H2O6)2 2- (aq) + H2O + 2H + (aq)

[0039] The result of this step is the coexistence of two immiscible phases, namely: one containing dichloromethane, ABS and dissolved tetrabromobisphenol-A; and the other, the aqueous solution with the antimony complex.

[0040] Step C: Insolubilization of ABS plastic

[0041] The mixture obtained in step B was transferred into 30 mL of diethyl ether as a non-solvent, resulting in the formation of three phases, namely: an organic phase consisting of the solvents and including tetrabromobisphenol-A; an aqueous phase including the antimony tartrate complex; and a fraction of ABS plastic material in solid form at the interface between the two liquid phases.

[0042] The non-solvent diethyl ether also serves as an extraction solvent for brominated molecules.

[0043] It was pre-cooled to 4°C for 12 hours to aggregate the ABS plastic particles into fine fibers, which facilitates their recovery by liquid filtration.

[0044] The fraction of solid plastic material obtained was cleaned with 10 mL of clean non-solvent diethyl ether, and oven-dried above the boiling point of solvents for 24 hours to remove residual solvents.

[0045] The two liquid phases were then separated by density difference. Antimony tartrate and tetrabromobisphenol A were recovered from their respective phases by evaporation / precipitation prior to analysis.

[0046] Table 2 below reports the characteristics of the different compounds: ABS, antimony compound and brominated compound before and after treatment by the process according to the invention.

[0047] Analytical methodSEC*XRF**Retention time (min)Mn (g / mol)MW (g / mol)PolydispersitySb (ppm)Br (ppm)Plastic material before extraction16.8741598972816161.763050090500Plastic material after extraction16.8831554942857731.83<5001980>Absolute variation0.009440941570.073000089320Extraction efficiency (%)98.4%97.8%

[0048] * Molecular weights and molecular weight distributions were determined using size exclusion chromatography. The SEC system consists of a Waters 1515 high-performance liquid chromatography isocratic pump, two Styragel HR 5E columns, and a refractive index detector. The eluent used is DMF containing 0.01 mol / L of LiBr, with a flow rate of 1.0 mL / min. The separation column and the refractive index detector are maintained at 60°C and 40°C, respectively. The calibration samples are commercial monodisperse polystyrenes.

[0049] ** The solid samples were analyzed by X-ray fluorescence spectrometry using the Malvern Epsilon 1 analyzer, with an X-ray tube and a silver anode capable of a maximum voltage of 50 kV and a current of 1 mA. The antimony (Sb) concentration was determined from the characteristic peaks at 26.359 keV (Kα) and 3.604 keV (Lα), while the bromine (Br) concentration was based on the peaks at 11.922 keV (Kα) and 13.29 keV (Kβ). Calibration was performed using reference samples prepared from ABS Resinex, pure antimony trioxide, and tetrabromobisphenol-A.

[0050] This example therefore demonstrates the ability of the process according to the invention to separately recover the different organic (Br) and inorganic (Sb) fillers and produce a new ABS plastic material which is depleted of its initial fillers down to the adequate minimum content and which is reusable in the plastics industry.

Claims

– A process for treating a used plastic part comprising at least one organic filler and at least one inorganic filler to recover separately: the regenerated plastic material, depleted in said organic filler(s) and in said inorganic filler(s); the organic filler(s); and the inorganic filler(s), characterized in that it comprises the following successive steps consisting of: adding to the part to be treated or to pieces thereof at least one organic solvent (S1), immiscible with water, a good solvent for said plastic material and capable of solvating said organic filler(s) and said plastic material and of releasing said inorganic filler(s), to obtain a mixture containing: in dissolved form, said plastic material and said organic filler(s); and in solid form in suspension, said inorganic filler(s);add to the mixture obtained in step (A) an aqueous solution of at least one extraction agent for said inorganic filler(s), said aqueous solution being capable of transferring by liquid-liquid extraction said inorganic filler(s) from said mixture to said aqueous solution, said inorganic filler(s) then being in a dissolved state in said aqueous solution;add to the two immiscible phases thus obtained in step (B) at least one solvent (S2) immiscible with water, miscible with said at least one solvent (S1), poor solvent for said plastic material and good solvent for said organic filler(s) to precipitate, following at least one solid phase, said plastic material in dispersed form while leaving said organic filler(s) in the mixture of said at least one solvent (S1) with said at least one solvent (S2), constituting an organic liquid phase, said inorganic filler(s) remaining dissolved in the aqueous solution, constituting an aqueous phase; recover said solid phase(s) of plastic material by solid-liquid separation; and isolate from each of said organic and aqueous phases obtained, separated by their difference in density, respectively said organic filler(s) and said inorganic filler(s). – Method according to claim 1, characterized in that the part to be treated is reduced into pieces, in particular of a dimension in its narrowest section less than 1 cm, for example from 50 mm to 0.5 mm, before engaging it in step (A). – A process according to any one of claims 1 and 2, characterized in that at step (A), the solvent or each solvent (S1) has a RED value less than 1, preferably less than or equal to 0.25, relative to the Hansen sphere of the plastic material. – A process according to any one of claims 1 to 3, characterized in that at step (A), the mass proportion of solvent (S1): plastic material is from 5:1 to 2:

1. – A process according to any one of claims 1 to 4, characterized in that step (A) is carried out at a temperature of 15 to 100°C or at the reflux temperature of the organic solvent (S1). – Method according to claim 5, characterized in that step A is carried out at a temperature of 15 to 40°C. – A method according to any one of claims 1 to 6, characterized in that step (A) is carried out at an absolute pressure of at least 10 5 Pa (1 bar). – A process according to any one of claims 1 to 7, characterized in that in step (B), in the case of several inorganic feeds, an aqueous solution containing different extraction agents is used, at a ratio of one extraction agent for one inorganic feed considered with a view to a simultaneous dissolution of said feeds, or several aqueous solutions containing each one extraction agent for one organic feed considered are used successively, said step (B) being able to be carried out at a temperature of 15 to 90°C. – A process according to any one of claims 1 to 8, characterized in that in step (B), an aqueous solution containing at least one additive selected from surfactants and phase transfer catalysts is used. – A process according to any one of claims 1 to 9, characterized in that at step (C), the solvent or each solvent (S2) has a RED value greater than 1, preferably greater than or equal to 1.25, with respect to the Hansen sphere of the plastic material, and a RED value less than 1, preferably less than or equal to 0.75 with respect to the Hansen sphere of the organic filler. – A process according to any one of claims 1 to 10, characterized in that step (B) is followed by a separation step by filtration of insoluble materials. – A process according to any one of claims 1 to 11, characterized in that: the plastic material is a thermoplastic material, such as acrylonitrile butadiene styrene, polypropylene, polyvinyl chloride, or high-impact polystyrene; the organic filler(s) is / are selected from brominated flame retardants, such as tetrabromobisphenol A; the inorganic filler(s) is / are selected from synergists of brominated flame retardants, such as antimony trioxide; the solvent(s) (S1) is / are selected from nitrobenzene, aniline, isoamyl acetate, n-butyl acetate, chloroform, dichloromethane, 2-phenoxyethanol, ethylbenzene, methyl isobutyl ketone, and cyclohexanone; the solvent (S2) is diethyl ether; the extraction agent is tartaric acid, citric acid or hydrochloric acid. – A process according to any one of claims 1 to 12, characterized in that it is carried out in batches, semi-continuously or continuously.