Method for depolymerising polyester
Provided is a method of depolymerizing a polyester, the method including adding a degradation agent to the polyester and then contacting the polyester with superheated water vapor.
1 . A method of depolymerizing a polyester, comprising:
adding a degradation agent including an alkali, an acid, a salt thereof, a mono-alcohol, a polyhydric alcohol, or a mixture thereof to the polyester, and
contacting the polyester with superheated water vapor.
2 . The method of depolymerizing the polyester of claim 1 , wherein
a temperature of the superheated water vapor is 250° C. to 450° C.
3 . The method of depolymerizing the polyester of claim 1 , wherein
the superheated water vapor is applied with an injection pressure of 0.1 bar to 2 bar.
4 . The method of depolymerizing the polyester of claim 1 , wherein
the depolymerizing is performed for 1 minute to 120 minutes.
5 . The method of depolymerizing the polyester of claim 1 , wherein
the alkali includes sodium hydroxide, potassium hydroxide, lithium hydroxide, ammonia, or a mixture thereof.
6 . The method of depolymerizing the polyester of claim 1 , wherein
the acid includes hydrochloric acid, nitric acid, sulfuric acid, carbonic acid, phosphoric acid, acetic acid, hypochlorous acid (HCIO), or a mixture thereof.
7 . The method of depolymerizing the polyester of claim 1 , wherein
the salt includes carbonate, hydrogen carbonate, phosphate, sulfate, sulfite, nitrate, silicate, hypochlorate, formate, acetate, citrate, oxalate, or a mixture thereof.
8 . The method of depolymerizing the polyester of claim 1 , wherein
the mono-alcohol includes methanol, ethanol, propanol, butanol, or a mixture thereof.
9 . The method of depolymerizing the polyester of claim 1 , wherein
the polyhydric alcohol includes ethylene glycol, n-propylene glycol, isopropylene glycol, diethylene glycol, polyethylene glycol, triethylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol, glycerine, benzyl alcohol, polypropylene glycol, pentaerythritol, trimethylolpropane, or a mixture thereof.
10 . The method of depolymerizing the polyester of claim 1 , wherein
the polyester is made by polymerizing a dibasic acid with alkylene glycol, and
the degradation agent is added at 0.75 mol to 3.0 mol per 1.0 mol of the dibasic acid in the polyester.
11 . The method of depolymerizing the polyester of claim 1 , wherein
the method of depolymerizing the polyester further includes,
the performing solid-liquid separation of liquid-phase alkylene glycol and a solid-phase dibasic salt from the depolymerization product obtained in the depolymerizing,
dissolving the solid-phase dibasic salt in water,
neutralizing an aqueous solution of the dibasic salt with an acid to precipitate a dibasic acid crystal, and
performing solid-liquid separation of the dibasic acid crystal from a precipitation product.
12 . The method of depolymerizing the polyester of claim 1 , wherein
the method of depolymerizing the polyester further includes removing impurities from the aqueous solution of the dibasic salt.
13 . The method of depolymerizing the polyester of claim 1 , wherein
the method of depolymerizing the polyester further includes recrystallizing the dibasic acid crystal.
14 . A composition for polymerizing recycled polyester, comprising a dibasic acid and an alkylene glycol, obtained by the method of depolymerizing the polyester of claim 1 .
15 . A recycled polyester prepared using the composition for polymerizing polyester of claim 14 .
16 . The recycled polyester of claim 15 , wherein
a color of the recycled polyester has an L-value of 60 or higher.