Nylon 66, nylon 46, and PET phase-transfer-catalyzed alkaline depolymerization at atmospheric pressure

The depolymerization of PET, nylon 66, and nylon 46 at high temperatures in an autoclave is well known in the patent literature. We sought to invent p rocesses for the depolymerization of PET, nylon 66, and nylon 46 in alkalin e solutions at low temperatures and atmospheric pressure. A method was deve loped for the depolymerization of polyethylene terephthalate (PET) which in volved the use of quarternary ammonium salt phase-transfer catalysts in sap onification processes at atmospheric pressure and temperatures as low as ro om temperature. Phenyltrimethylammonium chloride, hexadecyltrimethylammoniu m bromide, trioctylmethylammonium chloride, and trioctylmethylammonium brom ide were found to be effective catalysts for the depolymerization of PET in 5% aqueous sodium hydroxide solutions at temperatures as high as 80 degree s C and atmospheric pressure to form terephthalic acid in yields as high as 93%. The catalyst could be recycled. The alkaline phase-transfer-catalysis approach was then successfully applied for the depolymerizations of nylon 66 and nylon 46. Benzyltrimethylammonium bromide was discovered to be an ef fective phase-transfer catalyst in 50 wt.% sodium hydroxide solution for th e conversion of nylon 46 to oligomers. The collected nylon 46 oligomers wer e repolymerized using solid-state polymerization techniques to form high-mo lecular-weight nylon 46. Nylon 66 fibers were depolymerized in the presence of benzyltrimethylammonium bromide in 50% sodium hydroxide to form oligome rs and a monomer. Adipic acid was isolated.