Methods for recycling cotton and polyester fibers from waste textiles
Systems and methods are provided that involve a subcritical water reaction to recycle the cellulose and polyester components of waste cotton and cotton/polyester blend textiles that would otherwise be discarded or disposed of. Specifically, the disclosed methods provide for treatment of the waste textiles to produce advanced materials including cellulose and terephthalic acid (TPA) with a low environmental impact. The cellulose and TPA that are produced are of a high quality allowing for production of regenerated cellulose and regenerated polyethylene terephthalate (PET) suitable for fiber spinning and textile applications.
1. A method of producing terephthalic acid (TPA) from a polyester waste textile material, the method comprising:
treating the polyester waste textile material in a subcritical water reactor at a temperature of about 105° C. to 190° C., a pressure of about 40 to 300 psi, or both for about 0 to 90 minutes, wherein a dissolved TPA and ethylene glycol (EG) is produced, and wherein a regenerated polyethylene terephthalate (PET) produced from the TPA has a peak temperature as measured by differential scanning calorimetry and an onset temperature as measured by thermogravimetric analysis within +/−5% of that of standard reference PET.
2. The method of claim 1 , wherein the regenerated PET produced from the TPA has the onset temperature as measured by thermogravimetric analysis within +/−1% of that of standard reference PET.
3. The method of claim 1 , wherein the regenerated PET produced from the TPA has the peak temperature as measured by differential scanning calorimetry within 2.3% of standard reference PET or the onset temperature as measured by thermogravimetric analysis within 0.2% of that of standard reference PET.
4. The method of claim 1 , wherein the treating in the subcritical water reactor comprises a pH ranging from about 10-14.
5. The method of claim 1 , wherein the treating in the subcritical water reactor comprises about 5% (w/v) sodium hydroxide.
6. The method of claim 1 , wherein the polyester waste textile material/water ratio is about 1:5.
7. The method of claim 1 , further comprising recovering the TPA.
8. The method of claim 7 , wherein the recovering the TPA is carried out using a pH adjustment of about pH 2-pH 4.
9. The method of claim 8 , further comprising treating the recovered TPA with ethylene glycol in a PET polymerization process to produce the regenerated PET.
10. The method of claim 9 , wherein the treating comprises an autoclave at temperatures about 290° C. with Antimony metal (Sb 2 O 3 ) as catalyst.
11. The method of claim 9 , wherein the regenerated PET has an intrinsic viscosity of about 0.620 dl/g.
12. The method of claim 1 , further comprising recovering the ethylene glycol.
13. The method of claim 12 , wherein recovering the ethylene glycol comprises vacuum distillation.
14. The method of claim 1 , further comprising recovering the TPA and recovering the ethylene glycol.