Process for recovery of aromatic acid and dihydric alcohol from waste

Abstract

Processes are disclosed for recovery and purification of dibasic aromatic acids from waste polyester film, fiber, bottles, manufacturing residues, and other manufactured articles. The processes comprises: depolymerization of polyester resin in a molten polyester resin containing solvent with superheated stem, and vaporization of the aromatic carboxylic acid and other volatile products of hydrolysis to obtain a vaporized mixture containing aromatic acid, dihydric alcohol, other volatile products of hydrolysis, and water. This vapor mixture is, advantageously, substantially free of less volatile and non-volatile impurities including metals, and many colored and color causing compounds, which are, typically, found in post-consumer polyester resins. Crude acid is, optionally, purified by hydrogenated in an aqueous solution at elevated temperatures and pressures in the presence of hydrogen and an insoluble metal-containing catalyst, which is thereupon separated from the aqueous solution, and purified dibasic aromatic acid recovered by crystallization and mechanical separation from the aqueous solution. Purified terephthalic acid has, typically, a L*-value in a rage of from about 95 to about 100, an a*-value in a rage of from about -1 to about +1, and a b*-value in a range of from about 0.5 to about 2.