Method for purifying contaminated polypropylene
A method for purifying reclaimed polypropylene, such as a polypropylene reclaimed from post-consumer use or post-industrial use, is disclosed. The method involves obtaining the reclaimed polypropylene and contacting it at an elevated temperature and pressure with a fluid solvent to produce an extracted reclaimed polypropylene. The extracted reclaimed polypropylene is dissolved in a solvent at an elevated temperature and pressure to produce a polypropylene solution, which is purified at an elevated temperature and pressure by contacting the polypropylene solution with solid media to produce a purer polypropylene solution. A purer polypropylene is then separated from the purer polypropylene solution.
1. A method for purifying a reclaimed polypropylene comprising:
a. obtaining the reclaimed polypropylene wherein said reclaimed polypropylene is selected from the group consisting of post-consumer use polymers, post-industrial use polymers, and combinations thereof;
b. contacting the reclaimed polypropylene at a temperature from about 80° C. to about 220° C. and at a pressure from about 150 psig (1.03 MPa) to about 15,000 psig (103.42 MPa) with a first fluid solvent having a standard boiling point less than about 70° C., to produce an extracted reclaimed polypropylene;
c. dissolving the extracted reclaimed polypropylene in a solvent selected from the group consisting of the first fluid solvent, a second fluid solvent, and mixtures thereof, at a temperature from about 90° C. to about 220° C. and a pressure from about 350 psig (2.41 MPa) to about 20,000 psig (137.90 MPa) to produce a polypropylene solution;
d. purifying said polypropylene solution at a temperature from about 90° C. to about 220° C. and at a pressure from about 350 psig (2.41 MPa) to about 20,000 psig (137.90 MPa) by contacting said polypropylene solution with solid media to produce a purer polypropylene solution; and
e. separating a purer polypropylene from said purer polypropylene solution;
wherein said second fluid solvent has the same chemical composition or a different chemical composition as the first fluid solvent.
2. The method of claim 1 , wherein the purer polypropylene is separated from said purer polypropylene solution at a temperature from about 0° C. to about 220° C. and a pressure from about 0 psig (0 MPa) to 2,000 psig (13.79 MPa).
3. The method of claim 1 , wherein the reclaimed polypropylene is post-consumer recycle derived polypropylene.
4. The method of claim 1 , wherein said reclaimed polypropylene is a polypropylene homopolymer or a primarily polypropylene copolymer.
5. The method of claim 1 , wherein said fluid solvent has a standard boiling point less than about 0° C. and greater than about −45° C. and a standard enthalpy change of vaporization of less than about +25 kJ/mol.
6. The method of claim 1 , wherein said fluid solvent is selected from the group consisting of olefinic hydrocarbons, aliphatic hydrocarbons, and mixtures thereof.
7. The method of claim 6 , wherein said aliphatic hydrocarbon is selected from the group consisting of C 1 -C 6 aliphatic hydrocarbons and mixtures thereof.
8. The method of claim 6 , wherein said aliphatic hydrocarbons and mixtures thereof is comprised of primarily C 4 aliphatic hydrocarbons.
9. The method of claim 6 , wherein said fluid solvent consists essentially of C 4 liquefied petroleum gas.
10. The method of claim 8 , wherein said fluid solvent is n-butane, butane isomers, or mixtures thereof.
11. The method of claim 1 , wherein said temperature in steps b, c, and d is from about 110° C. to about 170° C.
12. The method of claim 1 , wherein said pressure in step b is from about 1,100 psig (7.58 MPa) to about 2,100 psig (14.48 MPa).
13. The method of claim 1 , wherein said pressure in step b is less than about 1,100 psig (7.58 MPa).
14. The method of claim 1 , wherein said pressure in step c is greater than about 1,100 psig (7.58 MPa).
15. The method of claim 1 , wherein said pressure in step c is greater than about 2,100 psig (14.48 MPa).
16. The method of claim 1 , wherein said solid media is selected from the group consisting of inorganic substances, carbon-based substances, and mixtures thereof.
17. The method of claim 16 , wherein said inorganic substances are selected from the group consisting of oxides of silicon, oxides of aluminum, oxides of iron, aluminum silicates, amorphous volcanic glasses, and mixtures thereof.
18. The method of claim 17 , wherein said inorganic substances are selected from the group consisting of silica gel, diatomite, sand, quartz, alumina, perlite, fuller's earth, bentonite, and mixtures thereof.
19. The method of claim 18 , wherein said inorganic substance is reclaimed glass.
20. The method of claim 16 , wherein said carbon-based substances are selected from the group consisting of anthracite coal, carbon black, coke, activated carbon, cellulose, and mixtures thereof.
21. The method of claim 1 , wherein said contacting of the polypropylene solution with said solid media is done in a packed bed of said solid media.
22. The method of claim 21 , where said packed bed is greater than 20 cm in length.