Kinetics of hydrolysis of poly(ethylene terephthalate) powder in sulfuric acid by a modified shrinking-core model

Poly(ethylene terephthalate) (PET) powder from waste bottles was degradated at atmospheric pressure in 3-9 M sulfuric acid below 150-190 degreesC for 12 h to clarify the mechanism for a feedstock recycle process. Terephthalic acid (TPA) and ethylene glycol (EG) were produced by the acid-catalyzed heterogeneous hydrolysis of PET in sulfuric acid. The TPA yield agreed with the degree of hydrolysis of PET, but the EG yield decreased with increasing sulfuric acid concentration because of carbonization of EG. The kinetics of hydrolysis of PET in sulfuric acid could be explained by a modified shrinking-core model for the chemical reaction control, in which the effective surface area is proportional to the degree of hydrolyzed PET, x, affected by formation and growth of pore and crack on PET powder. The apparent rate constant was proportional to the reciprocal of the particle size and the activity of sulfuric acid, and the activation energy was 88.7 kJ/mol.