Waste plastic density separation
Methods and systems for separating mixed plastic waste are provided herein. The methods generally comprise separating the mixed plastic waste into a PET-enriched stream and one or more PET-depleted streams. The separating may be accomplished using the combinations of two or more density separation stages. Exemplary density separation stages include sink-float separators and centrifugal force separators. The PET-enriched and PET-depleted streams may be recovered and/or directed to downstream chemical recycling processes.
1 . A waste plastic separation method comprising separating a mixed plastic waste (MPW) into a polyethylene terephthalate (PET)-enriched stream and a PET-depleted stream, wherein said PET-enriched stream comprises at least 70 weight percent PET on a dry basis and at least 0 . 1 weight percent and not more than 10 weight percent halogens on a dry basis, wherein the PET-enriched stream has a microorganism content of less than 10 5 CFU/g.
2 . The method of claim 1 , wherein said PET-enriched stream is also enriched in PVC and said PET-depleted stream is also depleted in PVC.
3 . The method of claim 1 , wherein said PET-enriched stream comprises not more than 2 weight percent of adhesives on a dry basis, and/or wherein said PET-enriched stream comprises not more than 4 weight percent plastic fillers and additives on a dry basis.
4 . The method of claim 1 , wherein PVC is not separated from said MPW or said PET-enriched stream as a PVC-enriched stream relative to said MPW or said PET-enriched stream.
5 . The method of claim 1 , wherein at least 50 weight percent of the PVC content in said MPW is separated from said MPW together with the PET into said PET-enriched stream.
6 . The method of claim 1 , wherein the PVC content in said PET-enriched stream is not separated from said PET-enriched stream prior to processing the PET in said PET-enriched stream in a chemical recycling process.
7 . A waste plastic separation method comprising:
(a) introducing mixed waste plastic (MPW) particulates into a first density separation stage; and
(b) feeding an output stream from said first density separation stage into a second density separation stage,
wherein one of said first and second density separation stages is a low-density separation stage and the other of said first and second density separation stages is a high-density separation stage,
wherein said low-density separation stage has a target separation density that is less than 1.35 g/cc and at least 1.25 g/cc,
wherein said high-density separation stage has a target separation density that is at least 0.01 g/cc greater than the target separation density of said low-density separation stage and that is at least 1.31 g/cc.
8 . The method of claim 7 , wherein the target separation density of said high-density separation stage is at least 1.33 g/cc and not more than 1.45 g/cc.
9 . The method of claim 7 , wherein said MPW particulates comprise PET and polyolefins in combination in an amount of at least 50 weight percent.
10 . The method of claim 7 , wherein said first density separation stage has a separation efficiency with respect to PET of at least 90 percent, and/or wherein said second density separation stage has a separation efficiency with respect to PET of at least 90 percent.
11 . The method of claim 7 , wherein said first density separation stage is a high-density sink-float density separation stage, and wherein said second density separation stages is a low-density centrifugal density separation stage.
12 . The method of claim 7 , wherein said first density separation stage is said high-density separation stage and said second density separation stage is said low-density separation stage.
13 . A waste plastic separation method comprising:
(a) feeding a stream of a caustic solution into at least one of a first or second density separation stages;
(b) introducing mixed waste plastic (MPW) particulates into said first density separation stage; and
(c) feeding an output stream from said first density separation stage into the second density separation stage,
wherein one of said first and second density separation stages is a low-density separation stage and the other of said first and second density separation stages is a high-density separation stage,
wherein no separate caustic component is introduced into said first density separation stage and/or said second density separation stage as a unit operation separate from said stream of caustic solution in step (a), and wherein said MPW particulates are not subjected to a separate antimicrobial processing stage, comprising addition of a caustic component, before being introduced into said first density separation stage.
14 . The method of claim 13 , wherein said caustic solution has a pH of greater than 8.
15 . The method of claim 13 , wherein said first density separation stage is a high-density sink-float separation stage, and wherein said second density separation stage is a low-density centrifugal density separation stage.
16 . The method of claim 13 , wherein said caustic solution is fed into said first density separation stage.
17 . The method of claim 13 , wherein said caustic solution comprises sodium hydroxide and/or potassium hydroxide.
18 . The method of claim 13 , wherein said caustic solution comprises potassium hydroxide.