Equilibria in the alcoholysis reactions of terephthalic esters and chemical valorization of polyethyleneterephthalate waste. I. Equilibrium constantsdetermination

The depolymerization of polyethyleneterephthalate (PET) by alcoholysis is a n easy operation and gives interesting prospects for the valorization of wa stes. The reactive species being composed of esters and alcohols, all possi ble alcoholysis reactions happen, whether wanted or not. Finally, a complex blend of many molecules follows. Practically, two great types of reactions occur: a reaction called "interch ange," and a reaction called "polycondensation.'' We have determined the va lues of global equilibrium constants of those two types of reaction. The va lues of polycondensation equilibrium constants are close to those estimated from the "equireactivity" principle. We did not observe any particular beh avior of monomer species. When reactants are the di- or mono-propylene glyc ols, the molar proportion of these glycolic radicals is higher in the free glycols than in the polyester chains. Both proportions are similar, when di ethylene glycol or 2-ethylhexanol are used. (C) 1999 John Wiley & Sons, Inc .