Method for supercritical fluid extraction of at least one plasticizer contained in a solid polymer material and associated equipment

Abstract

The present invention relates to a method for the supercritical fluid extraction of at least one plasticizer, in particular of phthalate and / or citrate and / or trimellitate type, contained in a solid polymer material, according to which fragments of said material are brought into contact, at least once, with said supercritical fluid for a given period of time, then said fluid is separated from said extracted plasticizer contained therein. Characteristically, said fragments are flakes that have a length greater than about 500 µm, in particular greater than or equal to about 700 µm and more particularly greater than about 710 µm and less than about 2000 µm.

Description

[0001] DESCRIPTION

[0002] Title :

[0003] METHOD FOR EXTRACTION BY SUPERCRITICAL FLUID OF AT LEAST ONE PLASTICIZER CONTAINED IN A SOLID POLYMERIC MATERIAL AND ASSOCIATED INSTALLATION

[0004] Technical field

[0005] The present invention relates to a method for the extraction by supercritical fluid of at least one plasticizer, in particular of the phthalate and / or citrate and / or trimellitate type, contained in a solid polymeric material in particular containing or consisting of polyvinyl chloride.

[0006] The present invention also relates to an installation allowing the implementation of this method.

[0007] Technological background

[0008] Phthalates are widely used plasticizers. They make it possible to obtain flexible and non-brittle plastics. They are known to be endocrine disruptors. The most dangerous and most widely used, particularly in the medical field, is di-2-ethylhexyl phthalate, also known by the acronym DEHP. DEHP has been gradually withdrawn from the market. It was used primarily with PVC, up to 60% by mass of the PVC mass.

[0009] It can still be found in the composition of materials used for medical devices such as catheters and blood bags, for example.

[0010] Citrates are high-value plasticizers that, like medical BTHC, can be very expensive. Their recycling would, in particular, reduce the production costs of polymeric materials containing them. Trimellitates, on the other hand, can be used in combination with or as an alternative to phthalates, particularly in applications where thermal stability and low volatility are important. Like citrates, they are considered to have a more favorable safety profile than certain phthalates, which are increasingly concerned about toxicity and health effects. The presence of plasticizers, such as phthalates, citrates, or trimellitates, prevents the recycling of plastics. It is therefore necessary to be able to extract them in order to reuse the polymer or polymer blend, possibly with another, less harmful plasticizer.

[0011] The publication entitled "supercritical CO2 extraction of phthalate plasticizers from PVC" by Yeong-Tamg Shieh & al published in the Journal of Applied Polymer Science, Vol 90, pages 4032 to 4037 in 2003 describes the extraction of the three phthalate plasticizers contained in a mixture of PVC and antioxidant. PVC has a degree of polymerization of 1000 and the antioxidant is a mixture of lead-containing compounds and mono, di or tri basic. The extracted phthalates are DOP (di-2-ethylhexyl phthalate also known by the acronym DEHP), DIDP (di-isodecyl) and TOTM (benzene-1, 2, 4-tricarboxylate of trioctyl). The extraction is carried out on small samples of given dimensions: 1 mm thick, 20 mm long and 10 mm wide. Each tested mixture contains 30 parts by mass of phthalate to 100 parts of PVC. The extraction time is 1 hour. The extraction temperature is 32°C or 35°C and the pressure is 3,000 psi or 5,000 psi.This publication indicates that the extrusion temperature of the PVC + DOP mixture has an influence on the flexibility of the material obtained and therefore its plasticization and that the flexibility of the material obtained has an influence on the extraction rate of DOP. The extraction rate is calculated based on the surface area of ​​the sample placed in contact with the supercritical fluid. This process is difficult to industrialize since it would be necessary to form films of plastic material and place them in contact with the supercritical fluid.

[0012] Technical problem to be solved

[0013] A technical problem that the present invention aims to solve is to provide a method that can be easily implemented on an industrial scale.

[0014] Another technical problem to be solved is to propose a process which makes it possible to obtain a treated plastic material containing less than 5%, preferably less than 4%, preferably less than 3%, preferably less than 2%, preferably less than 1%, preferably less than 0.5%, and even more preferably less than 0.1% by mass of plasticizer, the latter being particularly suitable for DEHP, the use of which is now prohibited by very strict regulations.

[0015] Another technical problem to be solved is to propose a process that allows the plastic material to be processed without too many steps and manipulation.

[0016] Another technical problem to be solved is to propose a process that uses only a supercritical solvent and not an organic solvent. Indeed, the use of an organic solvent requires further treatment and can be considered as waste.

[0017] Another technical problem to be solved is to propose a process that allows the plastic material to be treated in less than 3 hours.

[0018] Another technical problem to be solved is to propose a process that does not cause any thermal degradation of the PVC. Indeed, PVC is a highly heat-sensitive polymer. Another technical problem to be solved is to propose a process that allows both the extraction of as much plasticizer as possible and the extraction of as little stabilizing agent(s) and / or additives commonly added to PVC as possible.

[0019] Said stabilizing agent is preferably chosen from organometallic agents derived from carboxylates (in particular, stearates, octanoates (2-ethylhexanoic), and oleates), phthalates, or sulfates. Preferably, said organometallic agents are chosen from carboxylate derivatives, more preferably fatty acid derivatives or soaps of stearate type, octanoate (2-ethylhexanoic), and / or oleate.

[0020] Said organometallic agent also contains at least one metal atom selected from calcium, zinc, barium, cadmium, lead and / or tin, preferably selected from calcium and zinc. The chemical state of the metal atom within the organometallic agent is well known to those skilled in the art and may vary depending on the type of metal and the structure of the organometallic compound. The metal-oxygen bond may therefore be of an ionic or polarized covalent nature.

[0021] Preferably, said stabilizing agent is a fatty acid (stearate, octanoate, oleate or their mixture) of calcium or zinc.

[0022] Indeed, these stabilizers are essential for the transformation of PVC since all transformation techniques use large quantities of heat to melt the PVC. It should be noted that the homogeneous addition of these stabilizers to the core of the PVC cannot be done by simple cold mixing. Therefore, when the stabilizers are extracted, it is necessary to incorporate them again through a process involving the melting of the PVC under the effect of heat (such as an extrusion process). This process would risk completely degrading the treated PVC (formation of an extremely viscous and sticky black matter) making its reuse impossible. Stabilizers are organometallic compounds; it is the metal ions (zinc and calcium in particular) that thermally stabilize the PVC. It is therefore mainly calcium and / or zinc that stabilize the PVC, the organic part (egfatty acids) which in particular helps to promote the dispersion of these metal atoms (ions or radicals) in the PVC. Another technical problem is to propose an extraction process which avoids or limits any risk of gelling of the plastic material under the effect of heat during extraction.

[0023] Another technical problem to be solved is to propose a process which makes it possible to avoid using a micronizer, in particular a cryogenic micronizer.

[0024] Summary of the present invention

[0025] The present invention relates, according to a first aspect, to a method for the extraction by supercritical fluid of at least one plasticizer, in particular of the phthalate type and / or of the citrate type and / or of the trimellitate type, contained in a solid polymeric material, according to which fragments of said material are placed at least once in contact with said supercritical fluid for a given duration and then said fluid is separated from said extracted plasticizer which it contains. Typically, according to the invention, said fragments are flakes which have a length greater than approximately 500 pm, in particular greater than or equal to approximately 700 pm and more particularly greater than approximately 710 pm and less than approximately 2,000 pm, in particular less than approximately 1,500 pm, in particular less than approximately 1,000 pm, and more particularly less than approximately 1,000 pm.It is understood that "about X pm" means that at least 90% of the fragments meet this length condition, in particular 95% of the fragments, in particular 98% of the fragments, in particular 99% of the fragments and in particular still 99.5% of the fragments. About also includes 100% of the fragments meeting the length condition of X pm.

[0026] In practice, the different types of plasticizers can be extracted simultaneously. It is indeed the merit of the inventors to have found that such a flake size allowed rapid and efficient extraction of the plasticizer, in particular DEHP, DEHTP, BTHC and TOTM, in particular DEHP, while preserving the technical qualities of the polymer, in particular avoiding thermal degradation of the polymer and reducing as little as possible the thermal stability of the treated polymer.

[0027] It is thus possible to process flakes from blood bags or catheters, which are medical waste that cannot currently be recycled due to the presence of plasticizers that are toxic to health and the environment.

[0028] The polymeric material is not limited according to the invention. It can be chosen from polyvinyl chlorides and mixtures containing at least 40% or 50% by mass of polyvinyl chlorides (PVC) and in particular at least 90% by mass of polyvinyl chlorides.

[0029] The degree of polymerization of the PVC is not limiting of the invention.

[0030] The PVC preferably contains, before treatment, at least one thermal stabilizer chosen from organometallic compounds, in particular zinc and calcium carboxylates, more particularly zinc or calcium stearates and zinc and calcium octanoates. These compounds remain in the PVC treated by the process of the invention, which is materialized by a stability to thermal degradation which is almost equal before and after the treatment according to the invention.The phthalate-type plasticizer may be chosen from orthophthalates, terephthalates, linear aliphatic phthalates, mixed phthalates, hydrogenated orthophthalates such as DINCH (Di-isononyl cyclohexane-1,2-dicarboxylate), as well as hydrogenated terephthalates such as DEHCH (Di-ethylhexyl cyclohexane-1,2-dicarboxylate), preferably chosen from orthophthalates and terephthalates, and more preferably from di-2-ethylhexyl phthalate (DEHP), di-isodecyl phthalate, di-isononyl phthalate, benzylbutyl phthalate, dibutyl phthalate, diethyl phthalate, dicyclohexyl phthalate, di-n-octyl phthalate, dimethyl phthalate, di-2-ethylhexyl terephthalate and mixtures of at least two of these plasticizers. Preferably, said plasticizer is di-2-ethylhexyl phthalate (DEHP).

[0031] The citrate type plasticizer may be selected from butyl tri-n-hexyl citrate (BTHC), acetyl tributyl citrate (ATBC), tributyl citrate (TBC), tri ethyl citrate (TEP), tri-ethylhexyl citrate (TEHC), and mixtures of at least two of these plasticizers.

[0032] The trimellitate type plasticizer may be chosen from trioctyl benzene-1,2,4-tricarboxylate (or trimellitate) (TOTM), linear trioctyl benzene-1,2,4-tricarboxylate (or trimellitate) (linear TOTM), triisononyl benzene-1,2,4-tricarboxylate (or trimellitate) (TINTM), and mixtures of at least two of these plasticizers.

[0033] According to a preferred embodiment, the plasticizer is DEHP or a mixture of plasticizers containing DEHP.

[0034] According to a preferred embodiment, the plasticizer is DEHTP or a mixture of plasticizers containing DEHTP.

[0035] According to another particularly preferred embodiment, the plasticizer is BTHC or a mixture of plasticizers containing BTHC.

[0036] According to another particularly preferred embodiment, the plasticizer is TOTM or a mixture of plasticizers containing TOTM.

[0037] The supercritical fluid is chosen from carbon dioxide, water, and their mixtures. Carbon dioxide is preferred.

[0038] Optionally, before extracting said plasticizer with said supercritical fluid, said flakes can be impregnated with a liquid solvent. This step is optional; it generates an extraction solvent which must then be treated.

[0039] The liquid solvent may be chosen from apolar solvents and in particular from toluene, tetrahydrofuran (THF), benzene, methyl or ethyl benzoate, xylenes, 2-phenylpropane, cyclohexane, n-hexane, pentane, cyclopentane, carbon tetrachloride, chloroform, ether oxides in particular diethyl ether and 4,4-dioxane, epoxidized plasticizers in particular monoesters derived from the transesterification of epoxidized soybean oil, in particular epoxy fatty acid methyl ester (EF AME) and mixtures thereof. According to a particular implementation mode, combinable with each of the aforementioned implementation modes, the set temperature for extraction is greater than or equal to 80°C, in particular greater than or equal to 85°C and less than 130°C and in particular less than or equal to 110°C.The extraction pressure is greater than or equal to 30 MPa and less than or equal to 60 MPa, in particular between approximately 30 MPa and approximately 50 MPa, preferably between approximately 30 MPa and approximately 45 MPa, more preferably between approximately 30 MPa and approximately 40 MPa, preferably equal to 37 MPa, 39 MPa, 40 MPa or 50 MPa. These conditions make it possible to quickly treat the polymeric material and to obtain a mass percentage of plasticizer remaining in the material which can be as low as less than 0.1% in the case of DEHP for example.

[0040] Advantageously, the set temperature is 110°C and the pressure 39MPa or 40 MPa, which allows the flakes to be treated in 2.5 hours. If the pressure is 50Mpa, the treatment time increases to 50 minutes.

[0041] The process can be implemented in batch or semi-continuous mode. Semi-continuous mode means a batch process applied to several extractors in parallel which allow, at the end of a batch, to initiate a next one and then to repeat the same operation, thus allowing continuous processing of the material. When implemented in semi-continuous mode, the flow rate of supercritical fluid, in particular carbon dioxide, is not limited according to the invention. This flow rate is expressed in kilograms of CO2 per hour per kilogram of polymeric material (PVC). Since the fluid can be reused, after extraction of the plasticizer, such a flow rate does not pose a problem. The present invention also relates to an extraction installation allowing in particular the implementation of the method of the invention. This installation is of the type comprising a supercritical extractor connected to a fluid reservoir.Typically, according to the invention, it further comprises a gas / liquid separator coupled to said extractor and which makes it possible to recover the gas / supercritical phase contained in said extractor and to separate said supercritical fluid from said extracted plasticizer and the gas outlet of said separator is connected to said fluid reservoir. The installation may further comprise an impregnation tank with a liquid solvent, mounted upstream of said extractor or said extractor also allows the impregnation of said material with a liquid solvent.

[0042] Advantageously, whatever the embodiment, the installation comprises a grinder whose outlet is coupled to a screening device, and possibly means for conveying the fragments leaving said screening device into said extractor. It is thus possible to grind the flakes on the extraction site and to treat them immediately, which avoids any chemical deterioration of the flakes, for example, upon contact with air.

[0043] According to a second aspect, the present invention also relates to a method for the extraction by supercritical fluid of at least one plasticizer, particularly of the phthalate and / or citrate and / or trimellitate type, contained in a solid polymeric material, according to which fragments of said material are placed at least once in contact with said supercritical fluid for a given duration and then said fluid is separated from said extracted plasticizer which it contains. Typically, according to this second aspect of the invention, before extracting said plasticizer with said supercritical fluid, said flakes are impregnated with a liquid solvent. This step makes it possible to obtain a residual mass % of plasticizer, in particular DEHP, in particular less than 0.1% with much larger flakes. Indeed, it is possible to obtain this same extraction yield with flakes which have a length less than or equal to 2 mm and greater than or equal to 1 mm.The impregnation time can be 1 hour. The set temperature for extraction with the supercritical fluid can be greater than or equal to 80°C or 85°C and less than or equal to 120°C and in particular equal to 95°C.

[0044] Advantageously, an extraction is carried out with the supercritical fluid, preferably under the aforementioned conditions, then the flakes are impregnated, which then form a mass. After the impregnation, which can advantageously last one hour, a second extraction is carried out by supercritical fluid, advantageously under the same conditions as above.

[0045] The liquid solvent, the extraction fluid, its flow rate, the polymeric material, the type of plasticizer are as described with reference to the first aspect of the present invention.

[0046] It is therefore possible to obtain a treated polymeric material (in particular a polymeric material containing PVC, more particularly PVC) containing less than 5%, preferably less than 4%, preferably less than 3%, preferably less than 2%, preferably less than 1%, preferably less than 0.5%, more preferably less than 0.1% by mass of plasticizer (preferably strictly less than 0.1%) by using fragments (or flakes) of polymeric material which have a length greater than 500 pm, in particular greater than or equal to 700 pm and more particularly greater than 710 pm and less than 2 OOOprn, in particular less than 1 500 pm, in particular less than 1 OOOprn, and more particularly less than 1 OOOprn and thus to avoid the use of a micronizer (in particular a cryogenic micronizer), which is particularly desirable in order to avoid the degradation of the thermal properties of the PVC,in terms of costs (purchase and operation), and ease of implementation.,

[0047] Preferably, the length of said fragments is between 500pm and 2 OOOprn. Preferably, the length of said fragments is between 500pm and 1500pm.

[0048] More preferably, the length of said fragments is between 500 pm and 1 OOOprn.

[0049] More preferably, the length of said fragments is between 700 pm and 1 OOOprn. More preferably, the length of said fragments is between 710 pm and

[0050] 1 OOOpm.

[0051] The initial quantity of plasticizer present in the polymeric material before treatment by the extraction process according to the invention is not limiting and may be between 5% and 60% by mass, in particular between 10% and 50% by mass, and in particular still between 25% and 40% by mass. By way of example, and in order to avoid any ambiguity, X% of plasticizer by mass means that a polymeric material before treatment having a mass of 100 g, contains X g of plasticizer.

[0052] According to a particular aspect, the invention relates to a method for the extraction by supercritical fluid of at least one phthalate-type plasticizer contained in a solid polymeric material, making it possible to obtain a polymeric material containing less than 1%, preferably less than 0.5%, more preferably less than 0.1% by mass of plasticizer, according to which fragments of said material are placed at least once in contact with said supercritical fluid for a given duration and then said fluid is separated from said extracted plasticizer which it contains, and in which said fragments are flakes which have a length greater than 500 pm and less than 1 OOOprn.

[0053] According to a particular aspect, the invention relates to a method for extracting DEHP contained in a solid polymeric material comprising PVC by supercritical fluid, making it possible to obtain a polymeric material comprising PVC containing less than 0.1% by mass of plasticizer, according to which fragments of said material are placed at least once in contact with said supercritical fluid for a given duration and then said fluid is separated from said extracted plasticizer which it contains, and in which said fragments are flakes which have a length greater than 500 pm and less than 1 OOOprn.

[0054] According to a particular aspect, the invention relates to a method for the extraction by supercritical fluid of at least one citrate-type plasticizer contained in a solid polymeric material comprising PVC, making it possible to obtain a polymeric material comprising PVC containing less than 5%, preferably less than 3%, more preferably less than 1% by mass of plasticizer, according to which fragments of said material are placed at least once in contact with said supercritical fluid for a given duration and then said fluid is separated from said extracted plasticizer which it contains, and in which said fragments are flakes which have a length greater than 500 pm and less than 2 OOOprn.According to a particular aspect, the invention relates to a method for the extraction by supercritical fluid of at least one trimellitate-type plasticizer contained in a solid polymeric material comprising PVC, making it possible to obtain a polymeric material comprising PVC containing less than 5%, preferably less than 3%, more preferably less than 1% by mass of plasticizer, according to which fragments of said material are placed at least once in contact with said supercritical fluid for a given duration and then said fluid is separated from said extracted plasticizer which it contains, and in which said fragments are flakes which have a length greater than 500 pm and less than 2 OOOprn.

[0055] The usual operating conditions of the extraction process of the invention are an extraction time of approximately 3 hours, a temperature of approximately 85°C, and a pressure of approximately 37 MPa. These conditions, although not absolutely limiting, allow a good compromise to be obtained between time, costs and extraction performance. The conditions can of course be varied and adapted to the needs and objectives of the user.

[0056] Definitions

[0057] The term "flake" designates, within the meaning of the present invention, a fragment of film. A flake thus has a thickness greater than or equal to 10 pm and less than or equal to 500 pm and in particular equal to 200 pm. This thickness corresponds in particular to the thickness of the envelope forming the blood bags.

[0058] The term "polyvinyl chloride" refers to any PVC regardless of its degree of polymerization as well as any mixture of PVC having different degrees of polymerization.

[0059] The term "set temperature" refers to the temperature of the means for heating the supercritical fluid in the reactor. These heating means can be an electrical resistance or a heat transfer fluid circuit. The term "extraction temperature" also refers to the set temperature of the heating means.

[0060] The terms "flakes" having a length greater than Xpm and less than Ypm" designate the fraction of flakes obtained, by double screening and which has passed through the grid having round openings of diameter equal to Ypm and which has remained on the grid having round openings of diameter equal to Xpm. This fraction can be obtained by any type of screening including screening with vibrations and nutation of the grids. A person skilled in the art is able to determine the screening parameters which make it possible to obtain a fraction predominantly (at least 50% by mass and preferably at least 70% by mass and more particularly at least 90% by mass) consisting of flakes having the length included in the desired range.

[0061] “Lower” or “greater” includes “less than or equal to” and “greater than or equal to,” respectively.

[0062] Brief description of the figures

[0063] Other characteristics and advantages of the present invention will emerge from the description of the particular and non-limiting exemplary embodiments of the present invention below, with reference to the appended figures 1 and 2, in which:

[0064] [Fig. 1] schematically illustrates an example of a device allowing the implementation of the method of the invention; and

[0065] [Fig. 2] shows a photograph of the flakes before extraction (right) and after extraction (left).

[0066] Description of examples of implementation

[0067] With reference to Fig. 1, a particular embodiment of an installation allowing the implementation of the method of the invention will now be described.

[0068] The installation comprises a fluid reservoir 1 (in this case, a carbon dioxide reservoir), an extractor 6 and a separator 7. In the particular embodiment presented here, the installation comprises a tank 5 which can be used for impregnating the flakes with a solvent. This tank 5 is optional. A hopper 2 allows the flakes to be introduced into a grinder (not shown). The ground / crushed flakes pass through the filter 3. A volume of flakes having the required size distribution is thus obtained thanks to the use of a suitable sieving device. Conveying means 4 allow the transfer of the possibly impregnated flakes to the extractor 6. The extractor 6 is connected to the fluid reservoir 1 by a pipe 63. The extractor is equipped with a resistor (not shown) and the installation also comprises a pump (not shown) which allows the fluid pressure in the extractor 6 to be varied.It is thus possible to make the fluid supercritical in the extractor 6. The extractor 6 is connected to the separator 7 by a pipe 61. The gas outlet of the extractor is connected to the fluid reservoir 1 by a pipe 62.

[0069] According to a variant, the sieve opens directly into the extractor 6 and the installation does not include an impregnation tank 5.

[0070] The operation of the installation will now be explained with reference to Fig. 1.

[0071] The flakes to be treated are introduced into the hopper 2. They are ground / crushed by a grinder and pass through the sieving device 3. The flakes of the desired size fall into the tank 5 which can be filled with a solvent (toluene, for example). When the impregnation time has elapsed, the impregnated flakes which form a mass are introduced into the extractor 6. If the tank does not contain any solvent, the flakes remain in the form of flakes and enter the extractor 6 by means of the conveying means 4.

[0072] The extractor is closed and filled with fluid from tank 1 using a pump. The temperature and pressure in extractor 6 are increased so that the fluid enters the supercritical state therein.

[0073] The supercritical fluid which has been in contact with the flakes and is therefore loaded with plasticizer then passes into the separator 7. In the separator 7, the temperature and pressure conditions are modified so that the fluid passes into the gaseous state and the plasticizer into the solid or liquid state. The fluid (carbon dioxide) is then returned to the tank 1 through the pipe 62. It is possible to proceed in batch or semi-continuous mode. In batch mode, a given quantity of fluid is introduced whereas in semi-continuous mode, it is a continuous flow of supercritical fluid which comes into contact with the possibly impregnated flakes and then leaves the extractor before being separated from the extracted substances and then reinjected into the extractor.

[0074] The conveying means 4 are preferably designed to allow the impregnated flakes to drain.

[0075] Description of an example of obtaining flakes

[0076] In all the following examples, the films are first ground using a GETECHA GRS 180 mill equipped with rotating blades placed on the rotor and stator and a grid whose openings have a given size. Flakes having a length greater than this size remain in the mill. Flakes having a length less than this size are then ground again in a second knife mill. These two mills have grids with round openings of different sizes; the first mill has a grid with openings of 5 mm in diameter while the second mill has openings of 1.2 mm in diameter. The flakes obtained have a length ranging from 500 to 2000 μm. These flakes can then be sieved to separate the particles according to their particle size. Sieving is carried out on a vibrating sieving device having a nutating movement.The residence time of the flakes in the sieving device is very short (a few seconds if possible) and the sieving is carried out continuously. The device has two grids with round openings which make it possible to separate the majority of flakes having a length greater than the diameter of the openings.

[0077] In the following example, the last grid has openings with a diameter equal to 500 pm and the penultimate grid has round openings with a diameter equal to 1000 pm. It can be seen that the fraction of flakes with a length less than 500 pm has a pink tint, which is not the case for the fraction remaining on the last grid and having passed through the penultimate grid. It would seem that the change in tint already indicates a physicochemical degradation of the PVC caused by the mechanical action of the crushers.

[0078] Example 1: Study of the influence of flake size distribution

[0079] The plastic material to be processed comes from shredded blood bags. It is a PVC + DEHP blend or a plastic material containing at least 65% PVC, DEHP, and possibly another plasticizer or additive. The raw waste is in the form of flakes that are 3 mm or longer. The plasticizer extracted in this example is DEHP.

[0080] The raw flakes were ground and then sieved. The range xy pm indicates that the flakes have a length greater than or equal to xpm and less than ypm. The flakes are sorted by continuous sieving (double sieve) to obtain the length within the given range. The results are grouped in Table 1 below. The flake size corresponds to the size of the flakes that are introduced into the extractor or into the impregnation tank if present. The temperature is the temperature of the resistance in the extractor. The extraction yield is calculated by weighing before and after extraction and separation. The % of plasticizer is determined by calculation.

[0081] The carbon dioxide flow rate is measured at the outlet of the separator, the carbon dioxide being gaseous (pressure approximately 4 Mpa) and ambient temperature (20°C).

[0082] [Table 1]

[0083] From Table 1, we see that for a duration equal to 3h30, the best extraction yield is obtained with flakes having a length greater than or equal to 1000pm and less than or equal to 1500pm. Smaller flakes do not a priori allow a better extraction yield to be obtained.

[0084] The inventors were interested in the shrinkage of the flakes during extraction. Indeed, extraction quickly leads to a change in the size of the flakes. This is due to the difference in density of PVC when it contains 25-30% of a plasticizer (in general the density is close to 1) and when it does not contain any (the density is then close to 1.4). Furthermore, when they are partly curled or twisted, they return to a flat shape during extraction.

[0085] Example 2: Study of the modification of flake size during extraction

[0086] The results obtained are grouped in Table 2 below. The definition of the value ranges is the same as that in reference to Table 1. During these experiments, the temperature of the extractor resistance is 85°C, the pressure is 37 MPa, the flow is between 30 and 43 Kg CO2 / H / Kg PVC and the total extraction time is 3 hours. [Table 2]

[0087] From the results in Table 2, it can be seen that a mass percentage of DEHP remaining in the plastic material of less than 0.010% is obtained; the flakes after extraction have a length of less than or equal to 500pm.

[0088] Furthermore, Fig. 2 clearly shows the reduction in size but not in shape of the flakes after extraction. The flakes before extraction are in the left figure and the flakes after extraction are on the right. There is a difference in size and opacity, with the flakes becoming opaque after extraction.

[0089] Here, the residual plasticizer levels were determined by chemical analysis. The protocol used includes dissolving a PVC sample in tetrahydrofuran (THF) in an ultrasonic bath, reprecipitating the PVC resin by contacting it with water, and then analyzing the organic fraction (THF plus traces of plasticizer) by GC-MS. The acronym GC-MS refers to analysis by gas chromatography coupled with mass spectrometry.

[0090] Example 3: Influence of flake size on the thermal properties of PVC treated by the process of the invention

[0091] PVC is a highly thermosensitive polymer. When it is added with a plasticizer, it becomes an elastomeric material that deforms easily under stress by absorbing a significant portion of the energy it receives. For these two reasons, the usual technique for reducing the size of PVC particles is cryogenic micronization. This technique makes it possible to form very fine particles of less than 500 pm and sometimes even less than 300 pm. Obtaining this type of particle size can only be achieved by using this technique. Since the specific surface area of ​​a powder increases when the average size of the particles that compose it decreases, the use of very fine powders can cause prohibitive problems due to the shear stresses applied by the processing tools (extruder for example). Indeed, the shear stresses applied to a powder are maximum at the surface of the particles.The larger the specific surface area, the higher the density of the powder, and the higher the quantity of particles in contact with the processing tools (screw and barrel of an extruder). The consequence is that the larger the specific surface area, the higher the total shear stress applied to the powder. This causes more heating and more thermal degradation and also causes very rapid gelation in the case of PVC. Once it becomes a gel, the PVC adheres strongly to the walls and requires significant pressures and constraints to pass through the volume of the extruder. The faster gelation occurs, the longer it takes for the PVC to travel through the volume of the extruder.

[0092] The influence of the size of the PVC particles treated according to the process of the invention on the thermal properties of the latter has been highlighted. The results are presented in Table 3 below.

[0093] The PVC to be treated contains between 30% and 40% DEHP by mass. The carbon dioxide flow rate measured as explained with reference to example 1 is 30 kg CO2 / H / kg PVC.

[0094] The micronized or non-micronized particles (flakes) were obtained from blood bag flakes as in examples 1 and 2.

[0095] The flakes, 90% of which by mass are smaller than 2000 pm, were obtained by cryogenic micronization. The extraction time is 60 min. The temperature T denotes the temperature of the extractor resistance.

[0096] Static thermal stability represents the time measured in minutes after which the PVC test pieces derived from PVC flakes treated according to the process of the invention are subjected to a temperature of 190°C and turn black. This change in color, visible to the naked eye, is a sign of the thermal degradation of the treated PVC. The test pieces are obtained by calendering and then pressing to obtain films 400 μm thick. These films are then cut into strips 30 cm long and 2 cm wide. The static thermal stability test is carried out in a Mathis oven. The test pieces rest on a movable drawer which gradually leaves the oven over a period usually of 60 minutes (or more) so that the first end of the strips undergoes a short time of exposure to heat and the other end undergoes 60 minutes of exposure to heat.

[0097] [Table 3]

[0098] In this example, the final DEHP concentrations are less than 0%, which shows that other compounds (additives) are also extracted in part or in full.

[0099] From Table 3, it can be seen that the static thermal stability of PVC treated by the process of the invention (an essential property of PVC) decreases as the particle size decreases. The duration of the above-mentioned extraction is short (1 h) and is not sufficient to achieve complete extraction of the plasticizer. It is therefore logical to expect that longer extraction times will further reduce the thermal stability of PVC treated according to the process of the invention, thus making it almost unusable.

[0100] These results confirm that it is essential to determine an optimum particle size to minimize extraction time while ensuring the maintenance of the highest possible thermal stability.

[0101] Here, the residual plasticizer levels were determined by calculation based on mass balance and by chemical analysis. The protocol used includes dissolution in an ultrasonic bath of a PVC sample in tetrahydrofuran (THF), reprecipitation of the PVC resin by contact with water and then analysis of the organic fraction (THF plus traces of plasticizer) by GC-MS. The acronym GC-MS designates an analysis by gas chromatography coupled with mass spectrometry.

[0102] Example 4: Process optimization

[0103] The decrease in flake length was taken into account in the experiments below, as well as the carbon dioxide flow and the temperature and pressure conditions in the extractor. The flakes used are the flakes which, during sieving, passed through the grid with openings of diameter equal to 1000 pm and which remained on the grid with openings of diameter equal to 710 pm. The results are grouped in Table 4 below.

[0104] [Table 4]

[0105] In view of the results in Table 4 above, it can be seen that for flakes with a length greater than or equal to 710 pm and less than 1000 pm, all the DEHP initially present is extracted. In this example, the final DEHP concentrations are less than 0%, which shows that other compounds (additives) are also extracted in part or in full. The greater the carbon dioxide flow, the more it allows the plasticizer to be extracted from the solid material; the latter will in fact stiffen during extraction, which will make it more difficult to extract the plasticizer. On the other hand, the reduction in size will facilitate extraction. As a result, it was not easy to achieve optimization of the parameters of the extraction process of the invention.The best extraction yield is obtained in 50 min at a temperature of 110°C, a pressure of 50 MPa and a CO2 gas flow of 150 Kg CO2 / H / Kg PVC (volume measured under the same conditions as in the examples mentioned above). A good extraction yield is also obtained in 2h30 at an extraction temperature of 110°C, a pressure of 39 MPa and a CO2 gas flow of 26-27 Kg CÛ2 / H / Kg PVC.

[0106] Example 5: Process with impregnation step before extraction

[0107] The influence of a toluene impregnation step before supercritical extraction was also studied. The flakes before treatment have a length of less than 2 mm. The flakes first undergo a pre-extraction with supercritical carbon dioxide at 95°C, 37 MPa for 1 hour. The flakes are then immersed in toluene for two hours and then drained to remove as much solvent as possible. The flakes then form an agglomerated mass. A second extraction with supercritical carbon dioxide is then carried out under the same operating conditions as the first. The percentage of DEHP remaining in the flakes thus treated is less than 0.1%.

[0108] Example 6: Extraction of a citrate-type plasticizer

[0109] The plastic material to be processed comes from shredded blood bags. It is a PVC + BTHC blend. The raw waste is in the form of flakes of a length equal to or greater than 4 mm. The plasticizer extracted in this example is BTHC.

[0110] The raw flakes were ground and then sieved. The range xy pm indicates that the flakes have a length greater than or equal to xpm and less than ypm. The flakes are sorted by continuous sieving (double sieve) to obtain the length within the given range. The results are grouped in Table 5 below. The flake size corresponds to the size of the flakes that are introduced into the extractor or into the impregnation tank if present. The temperature is the temperature of the resistance in the extractor. The extraction yield is calculated by weighing before and after extraction and separation. The % of plasticizer is determined by calculation.

[0111] The carbon dioxide flow rate is measured at the outlet of the separator, the carbon dioxide being gaseous (pressure approximately 4 Mpa) and ambient temperature (20°C). [Table 5]

[0112] In view of the results in Table 5, it can be seen that the process of the invention also makes it possible to extract very large quantities of citrate-type plasticizer in a short time.

[0113] Example 7: Extraction of a terephthalate-type plasticizer

[0114] The plastic material to be processed comes from shredded blood bags. It is a PVC + DEHTP blend. The raw waste is in the form of flakes of a length equal to or greater than 4 mm. The plasticizer extracted in this example is DEHTP.

[0115] The raw flakes were ground and then sieved. The range xy pm indicates that the flakes have a length greater than or equal to xpm and less than ypm. The flakes are sorted by continuous sieving (double sieve) to obtain the length within the given range. The results are grouped in Table 6 below. The flake size corresponds to the size of the flakes that are introduced into the extractor or into the impregnation tank if present. The temperature is the temperature of the resistance in the extractor. The extraction yield is calculated by weighing before and after extraction and separation. The % of plasticizer is determined by calculation.

[0116] The carbon dioxide flow rate is measured at the outlet of the separator, the carbon dioxide being gaseous (pressure approximately 4 Mpa) and ambient temperature (20°C).

[0117] [Table 6]

[0118]

[0119] In view of the results in Table 6, it can be seen that the process of the invention also makes it possible to extract very large quantities of terephthalate-type plasticizer in a short time.

[0120] Example 8: Extraction of a trimellitate-type plasticizer

[0121] The plastic material to be processed comes from shredded blood bags. It is a PVC blend containing between 30 and 40% plasticizer, mainly TOTM, and less than 2% liquid additives. The raw waste is in the form of flakes of a length equal to or greater than 4 mm. The plasticizer extracted in this example is TOTM.

[0122] The raw flakes were ground and then sieved. The range xy pm indicates that the flakes have a length greater than or equal to xpm and less than ypm. The flakes are sorted by continuous sieving (double sieve) to obtain the length within the given range. The results are grouped in Table 7 below. The flake size corresponds to the size of the flakes that are introduced into the extractor or into the impregnation tank if present. The temperature is the temperature of the resistance in the extractor. The extraction yield is calculated by weighing before and after extraction and separation. The % of plasticizer is determined by calculation.

[0123] The carbon dioxide flow rate is measured at the outlet of the separator, the carbon dioxide being gaseous (pressure approximately 4 Mpa) and ambient temperature (20°C).

[0124] [Table 7]

[0125] In view of the results in Table 7, it can be seen that the process of the invention also makes it possible to extract very large quantities of trimellitate-type plasticizer in a short time.

[0126] Generally, the final plasticizer concentration is almost independent of the initial plasticizer concentration. This means that moderate variations in the initial plasticizer concentration do not affect the final concentration results.

[0127] Example 9: Study of the extraction of thermal stabilizers

[0128] The metal concentration was measured in PVC flakes with a size greater than 500pm and less than 1000pm before and after treatment according to the process of the invention. In this example, the supercritical CO2 extraction time is 50 minutes, the CO2 flow rate is equal to 6 kg CO2 / hour / kg PVC, the pressure is 500 bars and the set temperature is 85°C. The same results are obtained with the parameters of the optimized version of the process of the invention (example 4).

[0129] Detection is performed by inductively coupled plasma (ICP) mass spectrometry after mineralization with strong acids. The metallic soaps present in the test sample are zinc and calcium stearates.

[0130] The results are grouped in Table 8 below.

[0131] [Table 8]

[0132] From the results in Table 8, it can be seen that, thanks to the extraction process of the invention, the metals remain in the PVC and are not extracted by the supercritical fluid during the process of the invention. These metals are the essential components of PVC stabilizers.

Claims

CLAIMS 1. Method for the extraction by supercritical fluid of at least one plasticizer contained in a solid polymeric material, according to which fragments of said material are placed at least once in contact with said supercritical fluid for a given duration and then said fluid is separated from said extracted plasticizer which it contains, in which said fragments are flakes which have a length greater than approximately 500 pm, in particular greater than or equal to approximately 700 pm and more particularly greater than approximately 710 pm and less than approximately 2,000 pm, and in which, before extracting said plasticizer with said supercritical fluid, said flakes are impregnated with a liquid solvent.

2. Extraction method according to claim 1, characterized in that said fragments are flakes which have a length greater than approximately 500 pm, in particular greater than or equal to approximately 700 pm and more particularly greater than approximately 710 pm and less than approximately 1,000 pm.

3. Extraction method according to claim 1 or 2, characterized in that said polymeric material is chosen from polyvinyl chlorides and mixtures containing at least 50% by mass of polyvinyl chlorides and in particular at least 90% by mass of polyvinyl chloride.

4. Extraction method according to any one of the preceding, characterized in that said plasticizer is a plasticizer of the phthalate type, in particular chosen from orthophthalates, terephthalates, linear aliphatic phthalates, mixed phthalates, hydrogenated orthophthalates, hydrogenated terephthalates, preferably chosen from di-2-ethylhexyl phthalate (DEHP), di-isodecyl, di-isononyl, benzylbutyl, dibutyl, diethyl, di-cyclohexyl, di-n-octyl, dimethyl, di-2-ethylhexyl terephthalate and mixtures of at least two of these plasticizers.

5. Extraction method according to any one of the preceding claims, characterized in that said supercritical fluid is chosen from carbon dioxide, water and their mixtures.

6. Extraction process according to any one of the preceding claims, characterized in that said liquid solvent is chosen from apolar solvents and in particular from toluene, tetrahydrofuran (THF), benzene, methyl or ethyl benzoate, xylenes, 2-phenylpropane, cyclohexane, n-hexane, pentane, cyclopentane, carbon tetrachloride, chloroform, ether oxides, in particular diethyl ether and 4,4-dioxane, epoxidized plasticizers, in particular monoesters derived from the transesterification of epoxidized soybean oil, in particular epoxy fatty acid methyl ester (EF AME), and mixtures thereof.

7. Extraction method according to any one of the preceding claims, characterized in that the set temperature for extraction is greater than or equal to 80°C, in particular greater than or equal to 85°C and less than 130°C and in particular less than or equal to 110°C and in that the extraction pressure is greater than or equal to 30MPa and less than or equal to 60MPa and in particular equal to 37MPa, 39MPa, 40MPa or 50MPa.

8. Extraction installation allowing in particular the implementation of the method according to any one of claims 1 to 7, of the type comprising a supercritical extractor (6) connected to a fluid reservoir (1), characterized in that it further comprises a gas / liquid separator (7) coupled to said extractor and which makes it possible to recover the gas / supercritical phase contained in said extractor (6) and to separate said supercritical fluid from said extracted plasticizer and in that the gas outlet of said separator (7) is connected to said fluid reservoir (1).

9. Extraction installation according to claim 8, characterized in that it further comprises an impregnation tank (5) with a liquid solvent, mounted upstream of said extractor (6) or in that said extractor (6) also allows the impregnation of said material with a liquid solvent.

10. Installation according to any one of the preceding claims, characterized in that it comprises a grinder whose outlet is coupled to a screening device (3), and possibly means (4) for conveying the flakes leaving said screening device (3) into said extractor (6).

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