METHOD FOR TREATING USED PLASTICS BY DISSOLVING THE POLYMERS AND PURIFYING THEM BY WASHING

Abstract

The present invention relates to a process for treating a plastic feedstock comprising polymers, comprising: a) a dissolution step involving placing the plastic feedstock in contact with a dissolution solvent, at a dissolution temperature of between 100 C. and 300 C. and a dissolution pressure of between 1 and 20.0 MPa abs, to dissolve at least a portion of the polymers of the plastic feedstock and to obtain a crude polymer solution; b) a step of washing by placing the crude polymer solution in contact with a dense solution, at a temperature of between 100 C. and 300 C., a pressure of between 1 and 20.0 MPa abs and at a mass ratio between the dense solution and the crude polymer solution of between 0.05 and 20.0, to obtain a washed polymer solution and a washing effluent; and then c) a step of recovering the polymers, to obtain a solvent fraction and a purified polymer fraction. FIG. 1 to be published

Claims

1. A process for treating a plastic feedstock, comprising: a) a dissolution step involving placing the plastic feedstock in contact with a dissolution solvent, at a dissolution temperature of between 100 C. and 300 C. and a dissolution pressure of between 1.0 and 20.0 MPa abs, to obtain at least one crude polymer solution; b) a step of washing by placing the crude polymer solution obtained from step a) in contact with a dense solution, at a temperature of between 100 C. and 300 C., a pressure of between 1.0 and MPa abs and at a mass ratio between the mass flow rate of the dense solution and the mass flow rate of the crude polymer solution which feeds step b) of between 0.05 and 20.0, to obtain at least one washed polymer solution and one washing effluent; and then c) a step of recovering the polymers, to obtain at least one solvent fraction and one purified polymer fraction.

2. The process according to claim 1, in which the dissolution solvent is chosen from organic solvents with a boiling point of between 50 C. and 250 C., preferably between 15 C. and 150 C., preferably between 20 C. and 110 C.

3. The process according to claim 1, in which the dissolution solvent has a critical temperature of between 90 and 400 C., preferably between 130 and 300 C. and preferably between 180 and 290 C., and a critical pressure of between 1.5 and 5.0 MPa abs, preferably between 2.0 and 4.3 MPa abs and preferably between 2.4 and 4.2 MPa abs.

4. The process according to claim 1, in which the dissolution temperature in step a) is between 150 and 250 C. and the dissolution pressure is between 1.5 and 15.0 MPa abs and very preferably between 2.0 and 10.0 MPa abs.

5. The process according to claim 1, in which the dense solution used in step b) has a density of greater than or equal to 0.85, preferably greater than or equal to 0.9, preferentially greater than or equal to 1.0.

6. The process according to claim 1, in which the dense solution used in step b) is an aqueous solution, which preferably comprises at least 50% by weight of water, preferably at least 75% by weight of water, preferably at least 90% by weight of water, very preferably at least 95% by weight of water.

7. The process according to claim 1, in which the washing step b) is performed at the dissolution temperature and the dissolution pressure.

8. The process according to claim 1, in which the polymer recovery step c) includes a solvent recovery section at a temperature of between 0 and 350 C., preferably between 5 and 300 C. and preferably between 10 and 250 C., and at a pressure of between 0.1 and 20.0 MPa abs, preferably between 0.1 and 15.0 MPa abs and very preferably between 0.1 and 10.0 MPa abs.

9. The process according to claim 1, in which the polymer recovery step c) includes at least one solvent recovery section under temperature and pressure conditions adjusted so as to be under supercritical conditions of the dissolution solvent.

10. The process according to claim 1, comprising a step E2) of extraction by placing the washed polymer solution in contact with an extraction solvent, at a temperature of between 100 C. and 300 C., a pressure of between 1.0 and MPa abs and at a mass ratio between the mass flow rate of the extraction solvent and the mass flow rate of the washed polymer solution of between 0.05 and 20.0, in which the extraction solvent is preferably an organic solvent which has a critical temperature of between 90 and 400 C., preferably between 130 and 300 C. and preferably between 180 and 290 C., and a critical pressure of between 1.5 and 5.0 MPa abs, preferably between 2.0 and 4.3 MPa abs and preferably between 2.4 and 4.2 MPa abs, to obtain at least one extracted polymer solution and one spent solvent.

11. The process according to claim 10, in which the extraction solvent is the same as the dissolution solvent and is at least partly, preferably totally, in supercritical form.

12. The process according to claim 1, comprising a step E1) of separating out the insoluble matter by solid-liquid separation, at a temperature of between 100 C. and 300 C., a pressure of between 1.0 and 20.0 MPa abs, said step E1) being situated between the dissolution step a) and the polymer recovery step c), and upstream or downstream of the washing step b), preferably upstream of the washing step b), and in which the step E1) of separating out the insoluble matter preferably includes an electrostatic separator and/or a filter and/or a sand filter.

13. The process according to claim 1, comprising a step E3) of adsorption situated between the dissolution step a) and the polymer recovery step c) and including an adsorption section operated in the presence of at least one adsorbent, at a temperature of between 100 and 300 C. and a pressure of between 1.0 and 20.0 MPa abs.

14. The process according to claim 1, comprising: a) a dissolution step involving placing the plastic feedstock in contact with a dissolution solvent, at a dissolution temperature of between 100 C. and 300 C. and a dissolution pressure of between 1.0 and 20.0 MPa abs, to obtain at least one crude polymer solution; b) a step of washing by placing the crude polymer solution obtained from step a) in contact with a dense solution, at a temperature of between 100 C. and 300 C., at a pressure of between 1.0 and 20.0 MPa abs and at a mass ratio between the mass flow rate of the dense solution and the mass flow rate of the crude polymer solution of between 0.05 and 20.0, said dense solution preferably being an aqueous solution, to obtain at least one washed polymer solution and one washing effluent; E2) a step of extraction by placing the washed polymer solution obtained from step b) in contact with an extraction solvent, at a temperature of between 100 C. and 300 C., at a pressure of between 1.0 and 20.0 MPa abs and at a mass ratio between the mass flow rate of the extraction solvent and the mass flow rate of the washed polymer solution of between 0.05 and 20.0, to obtain at least one extracted polymer solution and one spent solvent; and then c) a polymer recovery step, to obtain at least one solvent fraction and one purified polymer fraction, said polymer recovery step preferably including at least one solvent recovery section under temperature and pressure conditions adjusted so as to be under supercritical conditions of the dissolution solvent.

15. The process according to claim 1, comprising: a) a dissolution step involving placing the plastic feedstock in contact with a dissolution solvent, at a dissolution temperature of between 100 C. and 300 C. and a dissolution pressure of between 1.0 and 20.0 MPa abs, to obtain at least one crude polymer solution; b) a step of washing by placing the crude polymer solution obtained from step a) in contact with a dense solution, at a temperature of between 100 C. and 300 C., at a pressure of between 1.0 and 20.0 MPa abs and at a mass ratio between the mass flow rate of the dense solution and the mass flow rate of the crude polymer solution of between 0.05 and 20.0, said dense solution preferably being an aqueous solution, to obtain at least one washed polymer solution and one washing effluent; E3) an adsorption step fed with the washed polymer solution obtained from step b) and including an adsorption section operated in the presence of at least one adsorbent, at a temperature of between 100 C. and 300 C. and a pressure of between 1.0 and 20.0 MPa abs, to obtain at least one refined polymer solution; and then c) a polymer recovery step, to obtain at least one solvent fraction and one purified polymer fraction, said polymer recovery step preferably including at least one solvent recovery section under temperature and pressure conditions adjusted so as to be under supercritical conditions of the dissolution solvent.

16. The process according to claim 1, in which the dissolution solvent is chosen from organic solvents with a boiling point of between 15 C. and 150 C.

17. The process according to claim 1, in which the dissolution solvent has a critical temperature of between 130 and 300 C., and a critical pressure of between 2.0 and 4.3 MPa abs.

18. The process according to claim 1, in which the dissolution temperature in step a) is between 150 and 250 C. and the dissolution pressure is between 2.0 and 10.0 MPa abs.

19. The process according to claim 1, in which the dense solution used in step b) has a density of greater than or equal to 0.9.

20. The process according to claim 1, in which the dense solution used in step b) is an aqueous solution which comprises at least 75% by weight of water.

Description

LIST OF FIGURES

[0163] The information regarding the elements referenced in FIGS. 1 to 3 enables a better understanding of the invention, without said invention being limited to the particular embodiments illustrated in FIGS. 1 to 3. The various embodiments presented may be used alone or in combination with each other, without any limit to the combinations.

[0164] FIG. 1 represents the scheme of one embodiment of the process of the present invention, comprising: [0165] a step a) of dissolution of the plastic feedstock 1 comprising polymers in a dissolution solvent 2, to obtain a crude polymer solution 3; [0166] a step b) of washing the crude polymer solution 3 with a dense solution 6, preferably an aqueous solution 6, to obtain a washed polymer solution 8 and a washing effluent 7; [0167] a step c) of recovering the polymers from the washed polymer solution 8 obtained from step b), to obtain a solvent fraction 13 and a purified polymer fraction 14.

[0168] FIG. 2 is a variant of the implementation of the process according to the invention represented in FIG. 1, comprising: [0169] a step a) of dissolution of the plastic feedstock 1 comprising polymers in a dissolution solvent 2, to obtain a crude polymer solution 3; [0170] a step E1) of separating out the insoluble matter, fed with the crude polymer solution 3, to obtain a clarified polymer solution 5 and an insoluble fraction 4; [0171] a step b) of washing the clarified polymer solution 5 by contact with a dense solution 6, to obtain a washing effluent 7 and a washed polymer solution 8; [0172] a step E2) of extraction of the washed polymer solution 8 with an extraction solvent 9, to obtain an extracted polymer solution 11 and a spent solvent 10; [0173] a step E3) of adsorption by placing the extracted polymer solution 11 in contact with an adsorbent, to obtain a refined polymer solution 12; [0174] a step c) of recovering the polymers from the refined polymer solution 12 obtained from step E3), to obtain a solvent fraction 13 and a purified polymer fraction 14.

[0175] FIG. 3 is a variant of the implementation of the process according to the invention represented in FIG. 2. In the embodiment shown in FIG. 3, the process comprises an intermediate step a) between step a) and step E1). The crude polymer solution 3 is placed in contact with an adsorbent in the form of divided solids for the purpose of obtaining a polymer solution 21 including the adsorbent in suspension and feeding the separation step E1). The adsorbent, introduced beforehand into step a), is then separated out and removed in the insoluble matter fraction 4.

[0176] Only the main steps, with the main streams, are shown in FIGS. 1 to 3, so as to allow a better understanding of the invention. It is clearly understood that all the equipment required for the functioning is present (vessels, pumps, exchangers, furnaces, columns, etc.), even if it is not shown.

EXAMPLES

Example 1 (in Accordance with the Invention)

[0177] 250 ml of n-pentane and 23 g of a plastic feedstock in the form of pink-violet-coloured beads 5 mm in diameter and based on polypropylene are introduced into a 500 ml autoclave equipped with a stirrer.

[0178] The autoclave is then closed hermetically and heated at 180 C. at a rate of 2 C. per minute, with stirring at 500 revolutions per minute (rpm). Once the temperature of 180 C. has been reached, the temperature and the stirring are maintained for 3 hours, at the autogenous pressure of 26 bar (or 2.6 MPa). After 3 hours, all the polypropylene is dissolved in the n-pentane. A highly coloured liquid phase, the crude polymer solution, is obtained.

[0179] 125 ml of water are then added to the system while maintaining the temperature at 180 C., the pressure at 2.6 MPa and the stirring at 500 rpm. These temperature, pressure and stirring conditions are then maintained for 5 minutes, before stopping the stirring. After stopping the stirring, the system then separates by settling. After 5 minutes at rest, the fluid system inside the autoclave separates by settling to form two phases at the end of the washing step. The upper phase, containing the polymer and corresponding to a washed polymer solution, is less coloured than the mixture before the washing step.

[0180] 15 ml of the washed polymer solution are taken up and placed in a crystallizing dish. The crystallizing dish is then placed in an oven at 180 C. and atmospheric pressure while flushing with nitrogen for 6 hours.

[0181] A slightly pinkish white solid is then obtained in the crystallizing dish.

Example 2 (not in Accordance with the Invention)

[0182] 250 ml of n-pentane and 23 g of a plastic feedstock in the form of pink-violet-coloured beads 5 mm in diameter and based on polypropylene are introduced into a 500 ml autoclave equipped with a stirrer.

[0183] The autoclave is then closed hermetically and heated at 180 C. at a rate of 2 C. per minute, with stirring at 500 revolutions per minute (rpm). Once the temperature of 180 C. has been reached, the temperature and the stirring are maintained for 3 hours, at the autogenous pressure of 2.6 MPa. After 3 hours, all the polypropylene is dissolved in the n-pentane. A highly coloured liquid phase, the crude polymer solution, is obtained.

[0184] 15 ml of the crude polymer solution are taken up and placed in a crystallizing dish. The crystallizing dish is then placed in an oven at 180 C. and atmospheric pressure while flushing with nitrogen for 6 hours.

[0185] A pink-violet-coloured solid is then obtained in the crystallizing dish. The solid obtained has a colour close to that of the beads of the initial feedstock.