GLYCOLYTIC RECYCLE OF POLY(ETHYLENE-TEREPHTHALATE) (PET)

In a comparison of PET waste recovery methods, glycolysis to monomer (DHET + low MW oligomers) represents a compromise between regeneration of starting ingredients by methanolysis or hydrolysis and direct remelt extrusion. It is less costly than the former and more versatile than the latter. The resultant easily filtered, low viscosity monomer is repolymerized to a useful molecular weight (MW), used as an ingredient for copolymers and used with additives for controlling luster, color, etc. Glycolytic recycle can be a batch or continuous process, the rate being dependent on temperature, catalyst, state of subdivision of the feedstock and the 2G/T ratio. In addition, the final monomer composition is controlled by the time of reaction and hold-up time after depolymerization. Low 2G/T ratios permit higher temperatures and faster reactions but result in higher MW oligomers. Side reactions occurring in the depolymerization are minimized by addition of a buffer as sodium acetate and limiting storage time at high temperatures. PET scrap suitable for glycolytic recycle includes production waste, fibers, film, flake, bottles, etc., but ingredients leading to side reactions, copolymers, end caps or color must be minimized for critical products and satisfactory rates of polymerization.