Simultaneous hydrolysis-oxidation mechanism of waste PET powder in nitric acid solutions.

New feed stock recycle process is required to promote the recycle of waste PET bottles. PET powder from waste bottles was degradated in 7-13 M nitric acid solutions under 100 degrees C at atmospheric pressure for 72 h. Terephthalic acid (TPA) and ethyleneglycol (EG) were produced by hydrolysis of PET in nitric acid solutions, and the EG was oxidized simultaneously to oxalic acid. The yield of TPA always agreed with the degradation of PET. However, the yield of oxalic acid was lower than that of the degradation of PET due to the oxidation of oxalic acid to CO2 in 13 M HNO3 at 100 degrees C. This is due to the faster rate of oxidation of oxalic acid than the rate of hydrolysis of PET. The kinetics of hydrolysis of PET in nitric acid could be explained by a modified shrinking core model for the rate determining, in which that the effective surface area was proportional to the degree of unreacted part (1-x), due to deposition of TPA produced. The apparent rate constant was also proportional to the activity of HNO3 and the activation energy was 24.2 kcal/mol.